Fortunately, the only repairs I've ever needed to do in really cold weather were flat tires - not really a hard job and all that was required was a tire lever, spare tube, and a pump. I keep a couple of those heat packs in the bottom of my pannier for such an event.

I think if I broke a chain I might be tempted to call for a pickup, but my advice is to carry the tools anyway. Better to have it and not need it etc, etc...