Since hubby and I are both nurses we're neurotic about safety, etc. So, I have come up with a pretty elaborate, yet compact first aid kit for our trail rides. I even have a first aid for horses book in it. I had to fight the urge to include everything I could possibly ever use - I would have needed an extra horse just to carry it. So I tried to stick to stuff I would need just to stabilize a person or horse initially until we could get them back home for further care. It fits in a large ziplock bag. Then I have a smaller ziplock bag with my "people comfort" supplies - chapstick, TP, matches, etc. I just keep both of these well stocked and in my saddle bag all the time, so I only have to pack food, etc. for each trip.
I was normal...then I got a horse.