i usually keep an "emergency pack" in my truck toolbox. 2-way radio, flares, handheld mirror, fully equipped first aid kit, hatchet, rope, butane lighter w/ refill. i keep that in one of my camelbacks with my 9mm shoulder rig for protection from overy curious wildlife/stray dog packs. for shorter rides where you're no more than a 10 minute ride from your vehicle, i leave the pack in plain view in the truck. i make sure i or someone else am wearing it for longer rides where the round trip would exceed 20 minutes.
an important part of your first aid kit is going to be large quantities of hydrogen peroxide, plenty of ace bandages for wrapping/making a splint, plenty of gauze, sealed/sterile surgical gloves and butterfly sutures from 1" to 6".
if you can afford it, a handheld GPS unit would quickly become your best friend for trail riding and might make the difference between life and death if you're in a situation where you're trying to talk in a life flight chopper to your location
