I keep a curry, hoof pick, and mane brush. The mane brush I use is actually a human hair brush but it works well on my horse's hair. I also have four brushes varying in stiffness from coarse to a soft finishing brush. I have a small face brush, a bag of rubber bands, Thrush Buster, a bot knife, and a pair of scissors.
There is a community bin my family's barn that contains hoof moisture, fly spray of various brands, healthy hair care, detangler, dish soap, horse shampoo and a collection of sponges, scrapers, and mits for bathing.
We keep a first aid drawer in the feed room, with a human first aid kit, as well as all the supplies to clean and dress a horse wound, some Bute and Banamine, Swat and SCR ointment. We have a stethoscope and digital thermometer. We also have duct tape, diapers and icthamol for the treatment of a hoof abscess.