A co-worker of mine hated driving to and parking at his local airport. So he would rent a car from the same airport for one day and then park it in his driveway until he had to leave for his trip. He never had to refill the gastank and put no more than 10 miles on the car. He racked up the FF miles without spending a ton of extra money.

Since he can now earn miles through airport shuttles, a rental car is not need anymore.