On a trip to Vegas one time I was following a friends car on my bike (motorcycle, Ninja 250). By sticking close the whole time (though not so close that I couldn't swerve around or stop if they did) I did well over 300 miles on one tank (just over 3 gallons).

Probably the stupidest and most dangerous thing I've ever done, but it cost me 10 bucks to get from Salt Lake to Las Vegas.