Tool list 2GO

I usually carry two boxes for tools and a couple of small boxes for odd ball uh like lugnuts for the spare tire and sometimes a ECU. With this and some luck (like limping the car to a location I could get parts) I've managed well the times things have gone wrong.

Full set of sockets (1/4, 3/8 and 1/2" drive) Roll of combo wrenches, Ignition wrenches, Hammer, A few pliers, one or two vise grips, wire cutters - usually lineman's plines, Allen keys. some sort of flashlight, extra leverage, at least two phillips and two flatheads, safety triangles (or flares but I've come to prefer the triangles after seeing truckers use them), jumper cables, 3/8 drive torque wrench (that's just where it lives - not an emergency item!), first aid kit, wheel chocks (4x4 blocks of wood saw diagonally).
Also some wire, some fuses, rags and usually a set of coveralls. There's always scraps of carpet in the trunk the boxes sit on and sometimes cardboard.

The most common repair I've had to do on the road is replace the alternator. The most extensive repair I can recall was when half a blade of the chrysler flex fan broke off and holed the radiator. Once I limped into Fredricksburg, bought a drain pain, fan, water pump, hoses, and battery and fixed it behind the parts store. They were very nice. Fortunately I was traveling down and had some baking soda in my backpack to help neutralize the battery acid. The most distrubing was a brake hose failure just after pulling into my Aunt's driveway in Fla. Fortunately, they're right outside of Pensacola and getting a hose made was just a matter of my uncle driving me into town.

So each person is different, but I'd say take the tools you use (or spares of the same) especially for alternators, tires, jump starts, cooling systems (hose clampls) and fuel systems. Also some way to caution other drivers if you are on the side of road.

+1 for another person without cell phones.