I rented a car last night because I thought I would be doing a bit of driving around. Only my flight got in late, and I have to leave early. So all I did was drive to the hotel (5 miles) and back. At what point do you start to think you need to put gas in the car? Is there a distance that is too short? I couldn't think of putting in half a gallon, and the gauge still showed full, but now I feel guilty.