Good list everyone. I have never been out in below -20 so can't comment about -40. I have spent weekends backpacking at +/- single digits. My main thing was to stay dry. I am very prone to sweating my ass off and usually have to dress down to stay dry and change shirts as soon as I get to camp.

One thing about your friends list, stay far away from cotton. It's comfortable, but deadly when wet. And it will not dry out for a long time.