Stuff in my truck's tool box:
extra set of belts
automatic transmission fluid
oil
fuel additive and anti-gel
extra fuel filter (incase fuel does gel)
starter fluid
washer fluid
socket and wrench set
vice grips, large cresent wrench, and some other tools
assorted bolts and fasteners
extra fuses, wire, and spare bulbs
winter front cover
100' extension cord
heavy duty jumper cables
set of tire chains
high lift jack
heavy tow strap
assorted tie downs
tarp (good for working under truck in snow)
flares
shovel, pulaski, combi tool, snow shovel
chainsaw (usually)
shop broom (for sweeping snow off)
SAR backpack
20 lb fire extinguisher
water fire extinguisher w/antifreeze mix

In the cab:
dog
mag light
spot light
250 watt inverter
cell phone and ipod chargers
cell phone antenna and powerbooster
50 watt Bendix King VHF radio
first aid kit
small fire extinguisher
couple of MREs and freeze dried meals
water bottles
bag of warm clothes
turnout coat
rain coat
shotgun
ice scraper
toilet paper
bunch of assorted batteries
spring loaded center punch (for breaking glass, but my past experiences with wrecks that i've been in i was always able to open a door, even while upside down)