For me it depends on where you will be driving. I often drive out into the middle of nowhere by myself. No cell service- no houses, little to no people.
I carry a basic craftsman tool set, wool blanket, shovel, flares (easy way to start a campfire), mountain bike (riding a bike out is easier than walking), tube of alumaseal radiator stop leak, an old fan belt, my old radiator hoses, kinetic energy rope, a logging chain, a spare ignition module (those things are crap and have went out on me several times before I put in a MSD ignition box), first aid kit, a tarp, tire plug kit, fire extinguisher, air compressor...
I'm sure I'm forgetting somethings.