Thick cotton towels take up a lot of space in your backpack. Save that space for other gear by using a PackTowl.
A large version, which measures 36 by 59 inches and weighs less than 10 ounces, can be rolled up to about the size of an 8-ounce water bottle. It also comes with a storage pouch.
It might not be quite as comfortable to use as a cotton towel, but a PackTowl ($13-$55, packtowl.com) is just as absorbent. It’s made with a soft microfiber fabric that soaks in up to four times its weight in water. A couple of swipes and you should be dry. The fabric is also thin, so the towel dries quickly.