>>622260Haven't seen anyone say this yet so I'll add my 2 cents. Sleep OFF the ground.
This is incredibly important. I don't mean sleep in a hammock up in the air (though done right that can keep you warm and dry.) I mean that you need a buffer between yourself and the ground. We've had at least a handful of people that forgot to have a sleeping pad to keep warm air flowing beneath their body at Winter NuggetFest. As a result they woke up with very cold backs or sides from the frozen ground sapping the heat from them. You can look up "Camping sleep pad" on Amazon and find them reasonably priced and just slide them in or under your sleeping bag.
This one looks pretty damn close to the ones we used in the Marine Corps
http://www.amazon.com/ALPS-Mountaineering-Foam-Camping-Regular/dp/B002QG1P6E/ref=sr_1_5?ie=UTF8&qid=1446816583&sr=8-5&keywords=camping+gear+sleeping+padsIf you're in a survival scenario and can't just go out and buy one, make yourself a hot coal bed, anyone that's seen the Movie Jeremiah Johnson, knows this can be dangerous and it's important to create a solid dirt buffer between you and the coals you'd be sleeping on.
http://backpackingtherockies.com/how-to-sleep-on-coals-using-a-survival-fire-bed/If you don't have access to fire, sleeping on a flat length of sticks sounds uncomfortable as hell but will keep your off the ground enough to avoid the previously mentioned heat stealing issues of laying on the ground in cold times.
Also here's a good guide to identifying and treating Hypothermia and other cold weather ailments. I'd recommend reading it over if you haven't camped in colder weather before.
https://www.princeton.edu/~oa/safety/hypocold.shtml 