I try and carry the most commonly used items with me, but I have a backpack packed with all sorts of good stuff that I try and take with me wherever I go, but leave it in the vehicle I am using.
Old Nike backback I've had for about 15 years filled with:
- First aid kit, complete with gauze, small selection of hypodermics, and peroxide
- Sunblock, small tube
- Lib balm
- deoderant
- Para cord. 100' black.
- Small tent spikes, 4
- Small folding saw
- Benchmade Nimravus fixed blade knife
- Medium sized needle and heavy black thread
- 8" Cresent wrench
- Channel lock pliers
- Wiha multi-tip insulated screwdriver
- Klein diagonals and needle nose
- 6' square tarp
- Thermal emergency blanket
- Road flares, 30 min, 4
- 8oz beef jerky, granola bars
- water purification tablets
- waterproof matches
- 750ml aluminum water bottle in side pocket
- 1 box, 50rds of RA45T +P
- Fenix TK11
- 20 replacement CR123 batteries in otter box
- Misc audio cables, adapters
- Various power cables for cell phones, ect
- USB, firewire, and ethernet cables of various types
- And a few other bits and bobs I can't remember right now
I can handle pretty much any situation that would come up with the items in that bag, and I consider it a very very good investment.