My list is pretty basic, no spare parts yet either.. Probably should get an icm since they are a pretty common failure.
tool set(metric and inch)
tow straps
yank strap
couple lengths of chain with hooks(not for removing vehicles..)
bottle jack
wheel chocks
2 come alongs
bunch of road flares
fluids(oil, atf, coolant, gear oil - all of which gets used and replaced)
couple tubes of rtv
good first aid kit
sleeping bag
winter clothing and rain gear
ground cloth
Glock w/ spare mags
3d mag lite
k-bar
2 mre's(use and replace them once a year)
water purifaction tabs and an empty water bottle
duct tape
2 gallon gas can(empty)
Having a burb is nice

I keep most of my camping gear in it as well. Since I don't run the 3rd row seat I've got two carpeted outdoor mats on the floor(the sort with the rubber bottoms). I don't wheel my rig so I'm not terribly worried about blowing parts on the trail. I'd like to eventually have a few more spare parts, but not too concerned.
I've used a lot of road flares up where I live.. curvey road that takes a toll on inattentive drivers and is out in BFE. Also pulled several trees off the road and this year am working on getting my chain saw up and running to keep in the truck when the weather hits. I do not keep water in my vehicle during the winter months.. don't want it freezing and bursting.
Started carrying the empty gas can after having someone come up to me in a parking lot for gas money. Told them no, but asked if they had a can for gas and where was their car(late 70's civic)

Filled up their 1 gal can and got them going. Of course I probably wouldn't have done this without the Glock handy.. can't be too cautious in this world
I do need to pick up a fire extinguisher...