As I said earlier I'm a care free commuter, but when travelling I always carry a camp towel. They're super absorbent, pack very small, and are very light weight.
They come in a lot of different sizes, but this small one that fits on a keychain is super handy-
http://www.rei.com/product/777958/ca...owel-155-x-155
You may want a bigger one if you sweat profusely, but I think this should do the job for most people.