You have lots of answers on clothes, so I'm going to add just one item that has helped me in Minnesota Winter Hunts including well below zero...Thermacare lower back wraps. Do NOT get the generic brands as they just do not work very well. Thermacare, however, last about 12 hours and will do a lot to keep your kidney area warm. If your first layer is a thin, wicking poly or wool, just put it on over that. They are too hot to put right against the skin. Personally, I just won't hunt in very cold weather again without them.