I want to have what I need to change a tire, disconnect a battery, fix a problem with a wire, repair a radiator leak, put out a kitchen or engine fire, jump start the vehicle or help someone else. I look at it from a task perspective. If I have a mechanical problem with the truck or the AC or furnace I am not going to fix it on the road but take it to a dealer.
I carry road flares, and tools for minor repairs (screwdrivers, pliers, vise-grips, spare fuses, wrench set, VOM meter, duct tape, electrical tape, pry bar, jumper cables, bailing wire, radiator stop leak, hand cleaner and rags). One a trip last year I used everything except the radiator stop leak, bailing wire, and the road flares.
There are quasi emergency situations where I want to be able to take care of the problem myself and that includes an electrical short, fire, flat tire, radiator leak, dead battery, blown fuse.