A baggy one piece outer layer helps a lot. I like using handwarmers inside my coat. I usually put one in each breast pocket of my shirt. I will put one on the back of my neck if it's brutal cold. Make sure you don't put it directly next to you skin. Some people are using those heat wraps that they use for sore backs. If i'm going in for an all day sit in cold weather I usually carry most of my clothes instead of wearing them in. I don't get sweaty that way. Sweat will get you every time. Move around every so often BEFORE you get cold.