OK Somebody's gotta say it. Go fixed gear. Ultra-reliability. Don't want to worry about fixing a broken chain? Measure the length and carry a spare one, they're not too heavy. There's no freewheel pawls to freeze, there's nothing that can't be fixed right then and there. If your brakes are ineffective in the snow, that's ok, you don't need them most of the time anyway. I barely use my brake. I did it for reliability and simplicity (which go hand in hand usually) and I have absolutely no regrets. Fixed gear wheels are non-dished and so they are inherently stronger no matter what the spoke count. They make perfect commuters. The only killer is if you have super-tough hills to navigate, but even that's managable. You get stronger after the first few rides anyway.

No, I'm not just being an advocate for fixed gear. I think it is a serious solution worth considering. The number of tools you have to bring along is dramatically reduced, and the likelyhood of breakage is minimal if setup properly.