I have a pair of Danners with 600gr thinsulate. Not as warm as the snowstalkers, etc, but better for walking in rugged terrain. Very supportive, comfortable and waterproof for crossing streams, etc.
I carry "boot blankets" in my pack and when I am sitting for a while, I pullem out and wear over the Danners. You can put those heat packs inside the bootblankets as well, although I haven't tried it.
I wear heavy knee high wool socks with poly liners--get the real wool min 85%, not the blends which sometimes only have a small amount of wool in em