For my Reatta and Eldorado around town/local cruise-ins/local car shows I carry a box of small tools and cleaning/detailing supplies. Our daily driver has small tools and emergency stuff (blankets, band aids, emergency lights, etc). When going to salage yards I carry "junking tools" in my "junking satchel". When traveling long distance (i.e. BCA Nat'l) I carry a larger tool box along with MAF, alternator, plugs & wires, oil & tranny fluid, coil/ignition pack, emergency stuff, etc., and of course my AAA Plus card.
Edit: I also always carry a non-a/c belt in my Reatta ever since Daves89 mentioned it a few years back.