I've given this issue a little thought and I think a good solution is a small dual sport bike (mine is a Yamaha TW 200). It is capable of carring some gear, going off-road, or travelling most roads.While full speed interstate travel would be unpleasant with this bike, it is small and light enough to cary on a hitch mounted dirt bike carrier. This makes it possible to have two vehicles without a trailer. I use mine to avoid towing a car behind an RV, but it would server well in an emergency. The bike gets 70+ miles per gallon (with a two gallon tank) and will handle some very rough terrain. I can even share fuel with my triple fuel stove using my camping fuel bottles as an extra reserve.

Marcy