I used to keep tools in my 2003 GMC extended 1/2 to. under the rear seat, they slid around a bit. Traded it in on a Ford Super Duty F250 4 X 4, now I Carry my cell phone and a extended warranty.
That is no fun.
Complete set of standard and metric 1/2 drive sockets
Tool wrap of craftsman wrenches standard and metric
Tool wrap with assortment of pliers, screw drivers, punches, and a couple of extensions.
Roll of electrical tape.
Assortment of tie downs
Jumper cables 2/0 guage for the F350
Plastic box of assorted electrical connectors, fuses, and small guage wire
4x4 cut into 12 in sections for cribbing
propane torch
GLOVES (mechanics and latex)
5 lb mini sledge
3 lb dead blow mallet
multimeter
Cam position sensor
All stored in canvas bags either behind or in the rear floor boards. They don't really move around. The only work I've had to do on my truck was remove the tunner when it locked up on a road trip and that didn't require any tools. My tool set has been invaluable to my friends and to strangers though. I've done everything from replace a boat engine to rebuild a toyota transfer case with just what I had on hand. My truck has 257k miles on it at some point it will let me down so it is best to be prepared.