I carry lot's of stuff in my truck. I am an offroader so I always try to prepare myself as best as possible, if you are in the bush many miles from the road you better be prepared I carry all this stuff from day to day driving also.

A set of sockets and wrenches
Hammers
Vicegrips
Channel locks
C clamps
Puller( for suspension work)
Breaker bar
Spare alternator
Spare starter
Spare hoses and belts
Spare tie rod ( plus special tool for removing it)
Lot's of bolts and nuts
Hi-lift jack
Bottle jack
4 ton come along ( hand winch)
Full size spare
Tire repair kit
Fire extinguisher
Jerry can
Full size Axe
Wood saw
Various oils and fluids

Plus I carry my personal survival kit and different survival items.