I travel with almost enough tools to completely overhaul a bike as well as spare tubes, patches, pump etc so mechanical problems aren't something I worry about too much.

My winter bike is a fixed gear and besides the fact this is my favourite kind of bicycle (summer or winter) it also does not suffer from the issue of frozen freewheels... I have had to torch a freewheel after having it freeze up at -30 C and that just isn't fun.

If things really went to hell on the commute I am always geared up well enough to hike it (I carry extra stuff in the paniers).