What I carry all the time:
1/4", 3/8", 1/2" socket sets, along with ratchets breaker bars, and extensions
Multiple sets of pliers, wire cutters and vicegrips
a few different hammers
assorted screwdrivers
hydraulic jack
TFI wrench
snap ring pliers
wire
Heat shrink tubing
solder
soldering iron
small inverter
lighter
mag lite
assorted hardware
hydraulic jack
hi lift jack
20' of chain
tow strap
tree saver strap
ratchet tie downs
bungie cords
a few screw pin shackles
carb cleaner
brake cleaner
maf cleaner
wd40
zip ties
electrical tape
25' air hose
bolt cutters
shovel
hose clamps
assorted air fittings
fuses
light bulbs
relays
tire plug kit
air compressor oil
motor oil
mercon III
antifreeze
tire pressure guage/air chuck
valve stems
measuring tape
vernier caliper
Jumper cables
files
rags
DMM
winch controller
butane
fire extinguisher
Stuff I will be adding to it soon:
air hammer/chisels
impact wrench
fuel pump relay
EEC relay
Test light
snatch block
starting fluid
sandpaper
I am also making a spare parts kit to carry sometimes, it will contain:
One complete set of axleshafts for the front
ujoints for front and rear driveshafts and front axleshafts
one hub
one spindle
one set of pre greased bearings (both sides)
2 front wheel seals
Belts
80w90
Grease gun/grease