I keep an o-ring assortment, spare CPS, spare fuel filter, spare fuel pump after some unexpected fuel pump failures, small floor jack, tow strap, spare serpentine belt, road flares, and a bunch of tools. For long trips I take extra oil (most of the time).
But sometimes I'm lazy and figure, my truck only has 475,000 miles on it, I don't need to waste the time loading up extra oil. I'm only driving 8 hours from home.
2002 F350 6-speed 444 CID. XLT, Heated Seat, 510,000 & counting.