For my cheapo, haul around in the pickup bed, tool set: Harbor Freight. Got one for $29 on sale, and it has enough 'stuff' in there to do minor fix its. Not top of the line in any sense of the word. But adequate for rarely used tools.
For my Harley Davidson, I started documenting all the size tools I used when doing regular maintenance. Then went to Sears and picked up duplicates (or small sets if on sale). They all fit in a small plastic tool box, which rests in the bottom of one saddlebag.
IMHO, any vehicle tool assortment, should include a length of fuel line, hose clamps, electrical tape, duct tape, and an assortment of wire ties. Just all depends on how far from civilization you plan on venturing. But it sucks being broke down on the side of a road/trail, when a screwdriver and pair of vise-grips could get you back.