Long road trip, I tend to go full size.
In the glove box, I go with something that can't go off just by pulling the trigger, e.g. HK P7, Browning Hi-Power, Colt 1911.
Somewhere else, I usually have XD45, Glock 22, or Sig P229.
Most frequently, I tote around my S&W 642.
I don't carry around any long guns, e.g. AR or AK, because I have a family and do not really have the room. I figure that if I end up in or near a situation that requires that kind of firepower, I am already screwed or I just need to be getting the hell out of there if at all possible.