Since gas has gotten so expensive, there's a plethora of information about saving gas mileage. I've been keeping track of mileage since I bought my car last year, and just watching my driving has resulted in lots of savings. My best record so far is over 40 mpg, which I achieved driving straight on a whole tank from my home in Seattle to Coos Bay, Oregon (for those familiar with the area, yes, I managed to drive my compact that far on a single full tank). I used cruise control the whole way and drove at the speed limit (or sometimes lower than the speed limit), and it made a major difference.
I'd suggest perusing the list to see if there's something you could be doing differently. At the cost of gas, saving a chunk of fuel economy could honestly pay off. Oh, and you'll probably be glad to notice that running A/C is a-okay by gas mileage; I know I'll be glad of that in August when I drive across country.