DRIVE SLOWER.
I try to maintain a nice, steady 40 miles per hour, the legal minimum on most highways. Also, I roll up the windows. It reduces wind resistance -- and noise. ("You can't hear those horns?" my wife asks, incredulous.)
8. SHOP WITH A RE-USABLE SHOPPING BAG.
And, if you can, walk to the store. ("It'll do wonders for your figure," I mention casually to the missus.)