I've shot at -40 C with an OM1. I used the TTL metering and the batteries would often die quickly. I changed them over with one I had in a pocket and after a bit of warming they would come back to life.
Dry cold causes static so be careful advancing the film and rewinding otherwise you get static streaks on the film. The film can also become brittle because of the cold so again be careful handling it.
When shooting I found that its best to wear 2 pairs of gloves. The outer pair can be really substantial affairs. The inner gloves should to be thin enough to allow you to operate the camera. This way you don't have to expose your flesh to the cold. Tape exposed metal parts of the camera so they don't come into contact with your skin. It will burn at best and at worst pull away great chunks of skin which is incredibly painful.
Condensation is the main thing to avoid when you take the camera from cold to warm. I kept all my equipment in its normal bag and when entering a building I'd just put the whole lot in a large sealed plastic bag. After a couple of hours I'd take it out. Going from warm to cold will mist up your optics wait a while and it will clear.
Look after yourself. Make sure you have adequate clothing in wicking layers on. Don't over dress either as sweat freezing can cause severe hypothermia. At temperatures below -30 C you can't afford to phaff around when taking pics keep on the move and keep warm. Look out for frost bite.