I'm a big fan of wool. The other thing is the sock liners. I fought off the cold last week in 15 degree temps. All I had was my boots and wool socks. I know with the sock liners I would have been fine. The sock liners keep moisture away from your feet. Physics 101 says when moisture is evaporating it robs the heat away from the surrounding objects. That same thing will keep your deer cool in the warmer weather if you keep a damp towel rapped around it.

In cold weather the first two things to keep warm are the head and chest. When they are warm blood get's sent to the other parts of the body. Next is your hand and then your feet. I find changing between standing and sitting with no weight on my feet does a pretty good job keeping my feet in check.