My shaved head. With all of the nerves and blood vessels in your head, you feel EVERYTHING. Especially if you've worked up a sweat. Just take my hat off and the side that's got the chill is where the winds coming from.
2nd best is a squeeze bottle filled with rock climbers chalk. I picked up a fairly big bag of it for a buck or two. Doesn't cake together, easy to see and doesn't have any oder. Bag has enough for years worth of hunting.