Helium in the tires, Pressurizing your cab while driving also helps, just buy a little compressor and hook it up to the HVAC unit and have it pump air through the vents. If you have a tonneau cover or a rape dome fill it with helium filled balloons or if you can achieve a tight seal just fill 'er up with helium without balloons. Drive with only 2 gallons of gas in the tank, less weight means more MPG""""''''"""s. Run only 2 quarts of oil in your engine, cuts down on the weight and it is better for the environment. Replace transmission fluid with olive oil. It is less dense than ATF and actually lubricates better. Extra virgin only.
Basic driving habits can also do wonders for your economy. Try throwing a book under the gas pedal so you can't achieve more than 1/4 throttle. Follow highway tractors extremely close, within three feet of the trailer to achieve a slipstream and windbreak effect. Drive ONLY with the wind, never against it. If you are driving into the wind adjust course accordingly. Remove your air intake and filter. They provide unnecessary restriction to the throttle body. Remember, The easier it goes in the more power you are making.
Thin out your gasoline with 1 cup of olive oil per gallon of gas for a beneficial lubricating effect and savings at the pump. If everything stays well lubed the engine will run better. Also try using four wheel drive all of the time. If all four tires are powered the engine has to work less, also you will save brake pads this way.