I carry everything I might ever need all the time!
I have a larger black plastic tool box I bought at walmart for like 20 bucks that takes up 3/4 of my cargo are and in it I keep:
2 large chains, 6 ratchet straps, 4 bungee cords, a cargo net for my roof rack, zip ties, a small craftsman socket set and star wrenches, a receiver with a d-shackle, a receiver with a 2" ball, heavy duty jumper cables, a mini air compressor, a 6 ton hydraulic jack, a tire iron, a 750w power inverter
then I also have a jeep duffle bag in the other 1/4 of my cargo area and it contains: a 2.5million candle power spot light, a small throw pillow, 2 fleece blankets and a roll of blue shop towels, a roll off parachute cord
then I have a craftsman tool bag in that 1/4 too it's for all my electrical tools:
folding standard and metric allen wrenches, folding star wrench set, a large and small phillips screw driver, a small and large standard screw driver, 2 rolls of electrical tape, a small tackle box of wire ends and connectors, a large and small pair of needle nose pliars, a small and large pair of channel locks, a pair of side cutters, a pair of diagonal cutters, a universal wire stripper 3 spare light switches, volt meter, and another small tackle box of fuses
and in the little cargo net on the right side I have a first aid kit.
Thats about it...Oh! and to top it all off (literally) I have a home made cargo shelf
I always try to be prepared.