Incidentally, for those really cold flying days, two words: heated socks. Gerbings and some other companies make socks that have heating elements (like an electric blanket) and are battery-powered. It's amazing how much better you feel overall just with warm toes.
If you wish to go with the non-powered version a pair of polypro sock liners with a smart wool or Thorlo sock over it helps a tremendous amount with the standard boot. My last squadron also bought us the nice wolverine brand winter boots. With that combination it's the only time I can remember my feet being warm in the back seat of the drumstick which can turn into a damn icebox while the guys in front are sweating (and ECMO1 controls the temp)