as for extras/ parts, carry a radiator hose or the means to splice or repair a ruptured hose, extra hose clamps of varying sizes, extra coolant// water, extra belt(s) work gloves, a roll of paper towels or shop towels, (and for us old folks that cant lay on gravel anymore without completely making us unable to get up and walk again, a mat of somesort to lay on while changing all of this stuff. tire plug kit and at least one if not two spare tires. Extra oil, transmission fluid, brake fluid and any other lifeblood fluid for your truck.
Some more mechanical harder parts to think about: a few u Joints, extra idlers or tensioners for the belts, a wheel bearing set, if you have manual hubs an extra hub and nut assembly.
Most of your trail repairs are not going to be much more involved than what is needed above, unless you are
@bobbywalter, then you can pack an extra engine/ drive train and only be down for about an hour or so while he changes it out with common hand tools
Some other odds and ends: bring a small shovel, you might need it to dig your self out, bring some 2x 12 sections to put under your jack or jackstands as the ground you are on will probably *not* be level.. Zip ties, duct tape, wd-40... you can temporarily (or permanently in some cases) fix a lot of ails with those items. your goal is not to make the truck OEM specs on the trail, but to get it back home or at least back out of the trail.
AJ