When I can, I commute the 18 mile round trip to work on my bicycle. It gets around 20 mile per 1000 calories. Unfortunately in Michigan, there's only about 8 months of good commuting weather.
LRR tires. Full fenders. Luggage rack with attachable basket for shopping (not sure it helps with aerodynamics). Rear view mirror. HID headlight and a couple rear blinking lights for safety.
* testing aerobars on it to see if this improves efficiency.