In two cars (Wife's and our classic) just the mfg's standard car tool kit, plus torche, plus high visibility jackets.
In my car I carry a fairly comprehensive toolkit of not my best tools. This includes 3/8th and 1/2 inch sockets, spanners, torx & allen keys, pliers, cutters, spare fuses, wire, nuts, bolts, washers, hose clips, tape, etc. Also spare water/antifreeze, oil & brake fluid. Also a tow rope
Basically pretty much a general collection (built up over time) of tools and basic bits and bobs that could possibly allow me to get myself out of trouble.
The one advantage of building such a kit is that when we go to Europe with the caravan I already have a decent ready made kit already in the car and I don't have to build a kit before these longer more remote journeys.
The size and content (shape) of any kit will be determined by what type of jobs/repairs you are prepared to tackle yourself vs calling for help.