If you are in a cold climate, some folks suggest you keep your tank filled. A filled tank does not get as much condensation, which can travel through your gas line and freeze. This can result in a non-starting car or a ruptured gas line. If you insist on the gallon-at-a-time method, make sure you put dry gas in your tank. Dry gas is a gasoline additive that absorbs water, and you'll only need it during the times when the temperatures get below freezing.
Switching to motorcycles, I always leave the tank filled with StaBil and dry gas over the winter. StaBil will keep the gas from going bad and the dry gas will keep condensation from rusting your tank from the inside out. When I used to ride classic bikes like the venerable Honda CB350, when I'd pick up a parts bike the tank would almost always be rusted out, the petcock was gummed up, and the carburetor had gummed-up jets and the floats were squashed from water getting trapped.