I second Denise's recommendation for the Timbuk2 bag. I recently purchased the small messenger bag (thanks to the great advice I received here!!), and I'm so happy with my purchase. It's perfect - not too big, and not too small, and, it has the waist strap. I actually just used it as my "purse" on a recent flight to NY and it held books, mags, water bottle, snacks, my wallet and a few other odds and ends. It's very durable and I'll probably end up purchasing another just for airline travel, and use the one I now own strictly for cycling.