For me, one of the best things I've done over several years, and several cars, is to really detail it up. I'm talking spend a weekend busting your butt on making the car as smooth as possible, to reduce wind resistance. I claybar the entire car from top to bottom, front to back, lens covers, glass, rims, etc... Then I put on a coat of polish, then two of wax, then one more of polish "have orbital". I rain-x all glass and lens covers. By the time I'm done, a paper towel can't even sit on the hood, it's that smooth. When driving, I barely have to touch the gas peddle to maintain speed, and the wind noise is virtually gone. Just a pleasant "shhhhh" over the car. I had my old 95' LS400 so slick, that when I sold it at 132k miles and 12 years old, it would still pull down 27mpg on the highwya, 19-20 around town. Plus, I also made sure the engine was in top shape, including the intake being spotless from carbon buildup.
But: if that's really you in your avatar...a simply little wink at any gas station in the world will probably get you a free tank of gas by a flattered guy.