We've been slackpacking for the last couple days just so we don't lose time.
We're getting back on the trail tomorrow, but just for one night. We'll be in Damascus on Monday, and might be looking for some work for stay with the negative temps rolling in.
As far as staying warm goes we bundle up. Nights that are colder than 20 we'll be in a clean pair of hiking socks with our heavy wool socks over them. Usually have on 2 base layer bottoms, and our down pants. We also have down booties from a company called 40 Below. We'll worth the extra 10 oz in weight. We also use mid weight base layer tops, wool sweaters, and our down/fleece jackets. We have insulated pads, and zero degree bags. I pull myself entirely into the sleeping bag, and that includes my head. At time I'll stick my nose or mouth out just to get some fresh air.
One trick to remember is that having to go to the bathroom makes you colder. If you got to go then go, and don't hold it in. There's really no key or hide secret. Proper gear is a must, knowing you limits, and knowing what to do are things to know.