This time of year I bring a terri-cloth hand towel with me. I just tuck it in my waist band while riding. It's really handy to have, not just for wiping the sweat but if you need to blow your nose, wipe grease or dirt of your hands after fixing something on your bike, clean sweat off your sunglasses, wipe of some blood, and also to dry sweat from my arms and hands. I have a stack of towels at home and bring a clean one on each ride. I learned this from a friend and long time mountain biker. I've gotten so accustom to having a towel with me now, I don't ride without one.