First, as others have pointed out, you do not need to stipulate the component, since it has no monetary value and is assume to be covered by 1) a component pouch or 2) a spellcasting focus/implement negates the need for a material component at all.
That said, I love coming up with things for a consistent and flavorful experience. So, if you want a list of things in your world that will work - not saying other things can't be substituted, but things that would be the most common and/or easily gathered by spellcasters to have in their component pouches - I'm game.
So I ask all of you ..... and ask for help:
- According to the type of enemy
Let's see what we can do...just as a side note, these whole categories of creatures are really too broad to pick one specific thing as there are creatures in those categories that are just too different. But I'll give it a shot.
a) Aberrations: piece of Blue Quartz (Calming & Harmonizing) or Celestite (Cleansing & Harmonizing)
b) Beasts: This is really too broad a category to make something consistent. Birds might be a birdcage. Aquatic creatures might be "air", but then what about aquatic mammals? For a simple, "works on any Beast", I'm going to say a collar or maybe some small cage or other type/representation of restraint.
c) Celestials: Any holy symbol of any evil deity. Any piece of a demon. "Unholy" [blessed by evil cleric] water.
d) Constructs: A wrench? Or chisel. A small hatchet or token of an axe [for wood golems]. Some simple tool or miniature replica of a tool that might be/have been used to construct them (and so could be used to dismantle them).
e) Dragons: Red/Gold: a crushed/powdered gemstone, Blue/Bronze: piece of wool & amber rod, Green/Copper: desert sand (beach sand will not work

, Black/Brass: a blooming flower, Silver/White: fire.
f) Elementals: For Air: some dirt or any stone. For Earth: a fan. For Fire: any amount of water. For Water: any amount of fire or earth -not stone, but
dirt so the water would become "trapped" in mud.
g) Feys: cold iron.
h) Fiends: Demons: holy water, holy symbol, silver, any piece of a demon, Devils: holy water, holy symbol, cold-wrought iron, any piece of a devil.
i) Giants: A teeny tiny carving of a giant (looks something like a dwarf) or mouse (dead is fine).
j) Humanoids: Kobolds/Goblins/Orcs/Hobgoblins: a blooming flower or butterfly. Bugbears/Gnolls/Ogres: a tuft of kitten fur or canary feathers + Trolls: Fire.
l) Monstrosities: ??? Individuals might be more interesting, but in general, how about just: pieces [minimum 1 each] of Carnelian (Warmth & Joy) and Citrine (Revitalizing & Cleansing)...sounds like a combination that "Monstrosities" would want to shy away from. Both are necessary, one or the other won't work alone.
m) Oozes: A glass vial, beaker, globe or bowl. Something that could [symbollically] contain them that can't be dissolved.
n) Plants: Fire.
o) undead: All: holy water, any holy symbol, any fire, Agate or [better] Ametrine, + for Wights & Wraiths: any silver + for Vampires: garlic. a mirror.
NPCs/classes will have to wait. Have some things to do.
