When I moved into the new barn here at our new house, I had my dad build me a wooden cabinet to store all the first-aid supplies. I do have a large assortment of wraps and towels as well, but I keep them in a separate trunk. ;-)
I keep the items I use most often on the bottom shelf. I have a variety of gauze pads in various sizes, rolled gauze, and surgical pads. Obviously, these are for underneath vetwrap and a standing wrap for cuts. I also have two large cotton rolls, but I have honestly had these forever (think 20 years) because I really have never needed them. I have found a gauze pad, gauze roll (if needed), vetwrap, and a quilt/standing wrap works the best.
I have bacitracin ointment, which is usually my got-to after Derma Gel (not pictured because I think it made its way into my show trunk) for any nicks, cuts, or scrapes. I have a thermometer, which has a long string and clothespin attached because trust me, you do not want to lose a thermometer in a horse's rectum. I use the petroleum jelly to insert said thermometer. I have a couple of empty syringes of various sizes for administering meds as needed. The mineral oil and Gas-X are always on hand just in case of a colic episode (I actually used up my mineral oil on a calf this spring, so this is a brand new bottle I hope to never need!). I have small samples of Bannix, which is a decent product, but I do prefer the Derma Gel. Scissors of course are always handy and I have a stethoscope to listen to gut sounds or heart/lungs as needed. The metal bowl is handy for washing out small cuts (I usually use Betadine, but my bottle's top broke so it is currently stored in a safe spot in the feed room with a makeshift cover. I don't want it to spill! And I always have a tube of Banamine, electrolytes, and Ulcergard on hand (though I just used up the last dose of Ulcergard for our last show - always one dose the morning of - and I am waiting for the new tube with my next Smartpak order. For some reason, I have a random tube of HA paste from Smartpak here which probably was a free sample somewhere and I ought to chuck it LOL!)
And on the very top shelf are the items that I really don't want to ever have to use haha! Thankfully, the only horse who liked to develop hoof abscesses was Reva and she is living up north doing low level pony club and distance rides now! Hoof abscess must haves include diapers, Animalintex poultice pads, ichthammol, Epsom salts, vetwrap, and duct tape! I have size 3 diapers here, which must have been the right size. I tend to stay with black or blue vetwrap but you can see I won a bunch of "fun" prints at a show last fall haha. I have never really needed to use the hoof packing much, so that is another item that has been in my first aid kit since the beginning of time with the rolled cotton LOL! I have Dial soap which is great for washing everything, cloth tape (I prefer duct tape with horses but this has been kicking around the barn for a while), and cotton balls. Bag Balm is a staple in the barn, right? But again, it is not usually my ointment of choice. And I have two balling guns that are really not my favorite to use, and one must be incredibly careful not to puncture the esophagus, but they do help when there is really no choice but to get several pills into a horse (aka Dreamy's episode with Lyme!).
So, that is my version of a well stocked first aid kit. Remember to always consult with your vet about learning to use any/all of the products I have shown here. Is there anything you use or have in your first aid kit that I should have?