Acid (Useful for trolls, and fire-resistant regenerating creatures).
Alchemist's Fire (Self-igniting replacement for oil, post first level).
Antitoxin (+5 Alchemical Bonus to Fortitude Saves vs. Poison. Take it BEFORE you need it! Lasts for one hour! Expensive, but can save someone's life).
TWO quivers of arrows, one attached to each side of the pack. From second until fourth level (whenever you can afford a Masterwork Mighty Composite Bow), get Masterwork arrows. They are cheaper, and have the same effect.
Backpack (this is a given).
Barrel (For water, if going on long wagon trips, and especially if crossing the desert!)
Bedroll (to sleep in, in cool weather, on, in warm weather, contains a light blanket for cooler weather, and serves as an emergency litter for unconscious companions, as well as padding and storage).
Winter Blanket (For colder weather, extra padding, and everything the bedroll does... In addition, wool is warm, even when wet).
Caltrops (If you're going to be pursued, slow them down! Generally left on the mounts).
Canvas (If going sailing, take extra sails!)
10' Chain (Cheap, easy to convert to a weapon, fairly light, nearly unbreakable, handy, and innocuous).
Chalk (Again, too small and light not to have on you at all times. Communicate underwater, etc.).
Class Tools (If you Craft, get a Masterwork set. If you're a Bard, get a Masterwork Instrument (if you use one) at second level. If you use spellbooks, make them waterproof, and make sure the ink is, too. Also keep a second copy safely, somewhere. See also Climber's Kit, Healer's Kits, Holy Symbols, and Thieve's Tools).
Climber's Kit (Too expensive at lower levels, and too heavy... At higher levels, have it custom built into a suit of Masterwork Studded Leather, for the +2 Climb Bonus).
Clubs (Free, 1D6 Blunt weapon. Use a torch, if the GM agrees).
Compasses (Again, not in the books, but since they were in common use by 1300, throughout Europe, they certainly fit into the Medieval period, and some GMs will allow them... If so, get a good one; shatterproof, weathproof, rustproof, etc. Add one to your survival necklace, another to your pocket, pouch, or girdle gear, one for your pack, and another in the saddlebags. If the GM says they don't exist, find a friendly Druid with the Discern Direction 0-level Orison, and have them make one for you! 1,000 GP for "At Will" use, IIRC).
Crowbars (+2 STR on opening checks. Masterwork versions are +4. If possible, combine a Handaxe, Hammer, balance it for throwing, then make the handle the crowbar; combine the prices, and make the whole thing Masterwork. Voila! Multi-tool and off-hand weapon!)
Dagger/knife (EVERYONE should have a simple cutting tool).
Everburning Torches (By second level, you can (as a party) afford a few. Get more than one, in case you run into a Darkness spell that's powerful enough to dispel it. Even so, keep a few REAL torches on hand for lighting things on fire).
Explorer's Outfit(s) (One at first level, but more, as funds improve - too many times Fireballs, acid traps, etc., have eaten a suit... Also, the extras, like scarves, bandannas, etc., can be handy).
Firestarters (Besides the tinderbox and flint & steel, magnifying glass, tindertwigs, and tinder, there are better ways of starting fires! Get a 1,000 GP Firefinger Cantrip for "At Will" use, and you have a more-or-less permanent "cigarette lighter"!)
Fishhooks (Less useful for fishing, and moreso for retrieving items).
Flint & Steel/Tinderbox (Everybody needs one, at first level, and multiples by second! These are too light and easy to carry; there is no excuse to be caught without fire!)
IF you have Simple Weapon Proficiency, and CERTAINLY if you have Heavy Armor, replace your Gauntlets with the Spiked kind... They cannot be disarmed, and are always "Ready". If you use a shield, one is probably enough.
Broad leather girdle, with pockets (Part of the Adventurer's Clothes; the girdle makes carrying weapons and mini-gear (like chalk) easier).
Grapnel/Grappling Hook (Useful for getting out of pit traps. The ones in the book are unrealistically heavy... Even a folding grapnel weighs no more than one pound!)
Hammer (WHY? Use the reverse end of the Handaxe!)
Handaxe (Even if you can't use it as a weapon, it is useful for chopping firewood, digging your way out of messes, and pounding in tent stakes! Even the Wizzez should have one!)
Healer's Kits (Past first level, everybody needs more than one! Keep one on the back of your girdle, one in your pack, and another in your saddlebags! Not only don't leave home without'em, don't get CAUGHT without'em!)
Holy Symbols (Wooden at first, buy metal at second. Keep both! Heat Metal/Warp Wood can destroy one. Wear one on your survival necklace, and keep the other(s) in your pocket or pack. Same for Druid/Ranger Mistletoe).
Holy Water (Same as Acid for Evil/Undeads who might be resistant or immune to Acid!)
Ink & Inkpens (A NECESSITY! Mapping, taking notes, sending messages...)
Keys (Manacles have keys. Many are "keyed alike". If you might get into some, why not have your own set of keys for getting out?)
Light Armor/"Paladin's Pajamas" (If you wear heavier armor, get a suit of lighter stuff to sleep in - once past second level, anyway. Often, you can get one "for free" from defeated opponents).
Light Warhorse (Get one at second level. It aids transport, carries gear, and can pull you up out of holes, on a good day. Don't bother with the untrained light horses, as the DC:20 Ride check to control them in combat is nearly impossible, at level one).
Locks, Amazing (These, with the chain, equal a light flail that doesn't look like a weapon, and can also get you out of a hole, secure your gear, or your horse! Amazing locks are too expensive at first level, but too hard for a Rogue to pick, too!)
Magnifying Glasses (Too expensive at first level, but useful for starting fires on sunny days, as well as for getting the +2 Circumstance Bonus to Appraisal of some items, so you might want to get a few, if skilled. Two can be used to form a simple spyglass, too).
Manacles, Masterwork (Too expensive at first, again, but too hard to escape, too, and can also hobble a prisoner, or horse, and secure gear).
Masterwork Mighty Composite Longbow +X (If you can use one, get one, ASAP).
Morningstar? (Better than a mace, for Clerics, as it does Blunt/Piercing damage).
Mug (Cheap, light, and handy to have, especially if you pack coffee or tea!)
Oil (First level, only! After that, use Alchemist's Fire, instead. It self-ignites, while Oil must be lit!)
Paper/Parchment (You need something to map, take notes, and write messages on!)
Pitons (Don't bother! See Climber's Kit!)
1 Gallon Iron Pot (Water in the wilderness is always suspect. Boil it for a minimum of 10 minutes, before drinking. Can also be used for putting out the campfire, cooking, and a host of other uses).
Two Beltpouches (Carry oil, alchemist's fire, acid, potions, thunderstones, tanglefoot bags, etc., where you can get to them. Attached to the girdle).
Ram (Crowbars are more useful, and far more portable).
Rope (50' hemp at first level, replaced with silk at second, as it is lighter, and gives +2 Rope Use. Keep the old hemp rope coiled on the saddlehorn, for lariat use).
Sacks (I never saw much use for these, wearing a backpack. YMMV).
Saddlebags (For storing horsecare items, extra food, and clothes).
Saddle/Weapons "Boot" (Not on the equipment lists, but that leather sleeve you put your lance, etc., down into).
Saddle, Military (For the +2 Ride checks when attempting not to fall off).
Scrollcase (Make sure it's waterproof, if you hafta buy cadles and dip it in wax, yourself! I prefer bronze. Also stores pens, ink, paper or parchment, and other smaller items).
Sewing Needles (So light there's no reason not to carry a few in tinderbox, pouches, girdle, pack, and saddlebags. Besides sewing, they can also be used as emergency lockpicks, with the -2 penalty).
Shovel (From second level on, always have one in the horse's weapons boot... Bury your dead, dig out the living, etc.)
Signal Whistle (At 0.1 pounds, it's too light not to have. Add one to the Survival Necklace, along with your Tinderbox!)
Signet Ring & Sealing Wax (Generally only useful for identifying that a note really came from you... Seal it with the wax, stamped with the ring's imprint. Yawn!)
10 Slings (Yes, TEN! Put two of'em through your boots as laces. Hang one on your girdle, or tuck it into a girdle pocket. Put one in a pouch, one in a pants or shirt pocket. Use the rest as straps to tie your bedroll, blankets, etc. Maybe use one to tie up long hair into a ponytail... I have NEVER had a PC be totally disarmed! Sure, rocks are only 1D3+STR, with a -1 to hit, but that's better than provoking attacks of opportunity with Subdual-only Unarmed Strikes! At higher levels, spend a few hundred on a Masterwork Sling, and the +1 Masterwork Bonus negates the -1 Penalty!)
Smokesticks (No cover to hide in? MAKE SOME! See Tindertwigs).
Soap (Besides being clean, you can also soap the stairs to stall enemy advances, etc.)
Spyglass (2x magnification isn't worth the price!)
Staves (Yes, it's staves, not staffs - and Magi, not Mages, as well - These, too, are free, 1D6 Blunts, and even better, if you are a two-weapon fighter, you can get two attacks with one, even at first level! Also, they are almost always "Ready" in hand!)
Sunrods (Glowsticks aren't really any more useful than Lanterns or torches, except that they can't be blown out, and don't ignite explosive gasses. Generally, one or two of these IN A PARTY is more than enough!)
Survival Necklace (Not on the equipment list... A woven-steel-wire ringsaw, wrapped in cloth to protect your neck, to the rings of which is attached a short length of easily-breakable light necklace chain. Hanging on this are your tinderbox, signal whistle, compass (if they exist in your campaign), a neck-knife or sharpened piece of steel, and a shiny piece usable as a signal mirror. Wear this whenever you adventure!)
Tanglefoot Bags (Semi-useful for tangling creatures at lower levels, but more & more useless as you advance).
Tent (Too expensive & heavy, at first level, but one/two people thereafter isn't bad, it keeps the rain off your head, and stays with the mounts, so the weight's little problem).
Thieves' Tools (Get the regulars at first level, and Masterwork at second. Keep the regulars in your survival necklace or tinderbox, and the Masterworks squirreled about your body... In a well-heeled party, someone besides the Rogue should carry an extra set, just in case. When the Rogue breaks theirs, you can triumphantly produce your replacement set, to cries of "Huh? What's a Paladin doin' with lockpicks?")
Thunderstones (Useful for deafening, and giving Spell Failure chances to casters... Deafness gives an Initiative penalty to any class...)
Tinder (Light, fluffy, easily-ignited stuff that will burn at high temperatures, and (preferrably) will work even in the wind & rain! The first is thin slices of dry wood. Even in a rain-drenched forest, you can split a log (remember the Handaxe?) and shave some off, but why wait until then? Shave some dry wood, coat the chips in flammable oil to prevent it from getting wet even in the rain, and voila; tinder! Alternately, you can wrap a small piece of tin or lead foil around a die (D6), remove the die, drip in some candle wax, sprinkle in some sawdust, repeat until the cube is full, then warm the foil until the wax melts, let it harden, then dump it out and roll it in the sawdust. One of these tindercubes will light easily, even in wind & rain, and burn hot enough to get a campfire started. Petrolatum (petroleum jelly, which exists if kerosene does, since gasoline is a by-product of kerosene's manufacture) can be "wrung" into a piece of cotton, and once it is "fluffed up", again, it will light, even when wet. Any/all of these can be packed into a small tinderbox, along with some simple wood chips, to help get a fire going quickly, even in the worst conditions! Finally, even if none of the above will work, those three candles in the tinderbox can usually be lit, and their flame then used to light a torch, or something bigger, like a campfire).
Tinderbox (A small box carrying flint & steel, along with some wood chips which can be easily ignited. String it on a chain or leather thong to hang around your neck, add three candles, and some other survival gear, such as a few fishhooks, needles, some thread, string, twine, cord, or line of some type. Make sure the box is waterproof, even if you have to oil it and seal it in wax, yourself. These aren't in the book, but even if the GM charges you 1 GP, it is worthwhile!)
Tindertwigs (AKA "Matches". Too expensive, but they light things faster. The only REAL use I can see for these are igniting a Smokestick. Otherwise, stick with flint & steel).
Torches (Even the Elves need one underground, and everyone needs a few for lighting oil, at first level. Also usable as a club, in a pinch. Get a few!)
Two weeks' Trail Rations (Yep, TWO WEEKS! Keep a day's-worth in your pouches, at least a week's-worth in your pack, and another week's worth in your pack at first level, and in your saddlebags, thereafter. Even if you have +20 Survival, having food will speed travel, since you can't forage/hunt except at half speed!)
Unarmed Strikes (Subdual damage, and provokes an Attack of Oppurtunity unless you have the Improved Unarmed Strike Feat, but you ALWAYS have it with you, so it's worth noting!)
Waterskins (EIGHT+ of the half-gallon variety - one gallon per person, per day (including cooking), or a quart per person per day for drinking, only. If you're eating trail rations (dried, for light weight), and existing on only a quart per day, expect to be THIRSTY! And don't forget the animals! Also, since there are no hard-sided canteens in D&D, expect to get "holed" waterskinns, occasionally. You need lotsa water for long trips, and always need extra skins... These can also be used as flotation bladders, or even air storage devices, in watery terrains).
Weapons: Spellslinger or not, everyone should have a bladed, blunt, missile, and light (grappling) weapon of their choice. Missiles are great for stopping spells. Blades are great for zombies, blunts are better for skeletons. Light weapons are all you can use when grabbed, grappled, swallowed, etc. Some weapons can fall into more than one of these categories (such as a shortsword).
Whetstones (A pound is ridiculous. Two of these per party is plenty. Share it with the one you love! Generally, unless you're going on a long trip, or chiseling your way through solid rock, this is one piece of equipment that you can probably get along without! It's generally not worth the weight).
