I'm not sure if anyone has mentioned this, but I went through Lifeguard first-aid training and the Firefighter who was teaching us all that he always has two essential things in any first-aid kit, maxipads and duct tape.
Maxi pads work much better than gauze. They are cheap, super super super absorbent, clean, flexible, great for large wounds, and stick easy to any sort of wrap that you want to put around them.
I plan on keeping at least a few in my med kit. They already saved me once when my daughter fell and split the skin on her forehead.
Something to keep in mind, anyway.
As for the duct tape, I probably wouldn't use that on a horse, but you never know when duct tape would come in handy.