I haven't started building my "kit" for my tracker just yet, but in my fullsize truck I carry, at all times:
folding shovel (proven to be the most useful so far)
axe
knife
tow strap
rope
PPE: coveralls, eye protection, gloves
basic hand tools (screwdrivers, wrenches, sockets, hammer, etc.)
portable air compressor
wd-40, other useful chemicals (can't remember off the top of my head)
duct tape, electrical tape
electrical splice connectors
cheater bar in the driver's door (or beater stick)
mag-lite
fire extinguisher
road flares
flagging tape
zip ties
SPARE BELTS AND HOSES
I am thinking about downsizing this to a more portable toolbox that can be moved from vehicle-to-vehicle and carry it in the tracker on the trail and keep it in the truck at all other times