Avoid the temptation to "top off" at the gas pump. When filling up, allow the machine to shut off automatically when it's full -- you'll hear a click, and the nozzle will stop pumping gas. Adding more gas wastes money because gasoline is often fed back into the tank via a vapor-recovery system, which prevents gas from escaping. So that extra bit isn't going to get your car any farther down the road. When the tank's full, stop filling up.