One free mileage help is a lightweight right foot. My truck gets 20% better mileage at 60 than at 70, but it's a brick compared to the slippery Neon shape.
I don't care if it takes seven hours to get from LA to San Francisco instead of six, but my wallet does. Just keep your tires pumped up, stay in the right lane, set the cruise control and dial up your favorite Sirius XM station.
Other benefits are less wear on the drivetrain and no more tickets!