Michael,
Collin's advice to have Leica "winterize" your camera in advance of the trip is good advice.
I believe there's an article on a shooter using M-cameras up in the cold wintery north in one of Leica's publications this month. I think it was Leica News...
Lastly, if you're wearing mitts (and I suspect you will be!
), do as Roger suggests... check out the rapidwinder, grip, and soft release combination. With the rapidwinder... you won't have to be trying to get your winding finger in behind the film advnce lever while trying to advance the film. The advance is at the bottom of the camera and it's long enough so that you can advance the film without looking. Once you get use to the wind and shoot... you'll find it quite efficient.
Cheers