My campaign information is stored in several formats - DNDBeyond/Roll20, Word, Excel, Handwritten Notes, Homemade Maps, etc... It spans 40 years and several editions. It contains lore/history, setting specific homebrew (rules, monsters, spells, items, races/heritages, classes, etc...). They have been slowly connected over the past few years to turn them into an offline Wiki.
If I had to guess, turning it all into a single useful Tome would result in a book of
well over 10,000 pages (maybe 20K?) of unique content. If we count redundancy it is easily 30,000 pages - maybe up to 50,000.
- I have about ~3,500 pages of recaps, timelines and other notes from prior sessions going back to 1982.
- I have writeups on each of my 101 major Powers/Gods, as well as on thousands of major NPCs. These are spread out, but there has to be 4000 pages there at a minimum.
- The descriptions of areas is rather insane - probably 5000 pages?. The setting of my campaign primarily is located on a world with a surface area that is 12 times the size of Earth - and has an Underdark (Dyson Sphere like) 'surface' that is nearly as large - and then there are hundreds of detailed locations throughout the planes and on other planets (though nothing is as detailed as the surface areas, and there are large areas of that world that have much lower levels of details). The biggest megadungeon that I've run several times in different instances of my world (there is a time travel / multiverse element to my setting) contains over 700 'rooms'. The document I used the last time I ran it was over 800 pages - and that is just the one megadungeon. I have other megadungeons I've run, as well as plenty of 'adventure' sized dungeons that have between 40 and 100 locations described.
- My spell, monster and magic item binders have spells from many editions. Some are digitized. Some are written on character sheets I filed away. Some are written on binder paper I took from my 4th grade classroom. They fill two bankers boxes filled with manilla envelopes. When I go back into the envelopes and I find something worth brigning back out, I digitize it (retype, photo->PDF/OCR with editing, etc...) and make it part of my digital world.
Most of this is specific to my primarily homebrew world. However, I have a few other settings that are documented in there as well, plus a number of standalone things. My christmas one shot files are expansive all by themselves.
I have two full (deep, wide, 6 foot tall) bookshelves oh physical content, and then a growing digital version that is distributed in many folders and documents.
And none of that counts the physical terrain, maps, miniatures, dice, tools, etc...