My first aid kit is huge, 2 filing cabinet draws full of stuff! I also have a little kit I take in the trailer and a smaller one for my saddle bags
Riding kit - Bute, vet wrap, wound wipe, wound cream, sanitary towel (for handy individually wrapped non-stick wound dressing), syringe, steri strips, expanding towel, human pain killers, foil blanket.
Trailer kit - as above but in bigger quantities plus, hibi scrub, surgical gloves, thermometer, manuka honey, cotton wool, duct tape, instant calmer, electrolytes, Thirst quencher, antibiotic cream, chemical ice pack.
The rest - I would have to look to be sure
there's more of the above and Gamgee, poultices, various creams/ointments/sprays, eyes drops, sterile water, saline, various cooling gels and liquids, bandages/tubigrip, a clean Tupperware box, wormers, sedaline, hoof armor, Ice packs (kept at home in freezer ready), ice bag (to use with ice cubes), knee wraps, heat boots, and a bunch of foot treatment things. Basically anything I get goes in and I just clear out old stuff once in a while