I carry enough basic survival supplies that I should be able to handle any small emergencies that come up.
Here's what goes in the pack:
Water (Camelback reservoir pack, so it's built in)
Cache goodies
Folder with cache printouts/maps of area (if I happen to have them)
Spare batteries (for GPS, camera and flashlight)
Flashlight
Glow-Sticks (orange/green/red)
Lighter
Waterproof matches
Poncho (small foldable poncho)
First Aid Kit (with bee sting and snake bite kits)
Toilet paper (!!!!!)
Collapsable shovel (like a little garden shovel that folds)
Compass
Cell phone
Camera
Whistle
"Power" snacks (M&M's and peanuts, powerbar, etc.)
Spare socks
Spare car/house keys
Emergency contact information card (laminated)
Leatherman multi-tool (pocket knife, screwdriver, etc.)
I believe that's all. I know it sounds like a lot, but I'd rather have more than I need than be stuck out in the wilderness in an emergency.