For true cold, "keep it simple" is a good motto. Keep spare batteries in a pocket next to your body. Forget about autofocus if it is inconsistent, use manual instead. Autofocus ought to work to -10 or -15 C, but the motor isn't very powerful, any lubricants tend to stiffen up, and other mechanical properties of lens components may change at truly low temperatures. If I know that I am going to shoot in standard cold situations (0 to -10 C), I leave my gear in the car trunk overnight. Plastic bag the camera before you bring it into the warm. If you want to shoot for multiple sessions, leave the camera in the car trunk in between, if you need to chimp, take only the card inside.