Pretty much what I need to work or emergency repair on anything short of dropping/replacing/rebuilding the engine-drivetrain.
Socket ratchet and extension set, 3/8-inch drive, 6-point (never needed 12-points since the 80's) 11mm to 22mm
Socket ratchet and extension set, 1/4-inch drive, 6-point up to 12mm
Combination wrench set up to 21.
Basic Pliers and screwdrivers
A pair of vise-grips
Multi-meter and assorted test leads (like alligator clips to allow me to clip to a point and probe a point far from it without an assistant).
AND AT LEAST A SCHEMATIC IN PDF FORMAT ON MY SMARTPHONE.
Above kit would allow me to work on light repair like electrical, alternator, power steering pump, starter, radiator, basic suspension remove and replace.
I used to leave my oil filter wrench at home because it's a routine maintenance thing, I went due for oil change in middle of my rRoute 66 trip. Quick oil change places did not carry my choice of oil (10W-30 or 10W-40) so I ended up doing it myself. Fortunately, I was at my cousins home and his strap filter wrench worked.
I could carry a 30-watt soldering iron too, but for emergencies, twisting/crimping/taping wire would work, too.
Funny...
I bought a Craftsman set for about $100 in 1987. A few years ago I realized I never had use for the 12-point and English sockets, and other parts. I sold them for $35. Not a bad resale value for half of the set..