I know this thread is a few years old, but I wanted to chime in for those who may still be reading it
(you can never have too much good advice floating around).
I've had great success staying warm, even without a snuggle buddy, by 1., staying the hell OFF the ground. Get off the ground any way you can-- hammock, pallets, cardboard, I've stuffed leaves into a trash bag and slept on that during the fall, etc. get creative!
2. drafts and wind SUCK, so barricade yoself in! even if it's just enough room for you to curl up or lay straight down on, make sure that where you are sleeping is as sheltered from wind and drafts as possible. You can be nice and toasty until a little gust of invisible icy shit sneaks up on you and steals all your hard won heat. This also goes for shifting positions in your sleep, but that's not as easily controlled.
3. keep your head, feet and hands as bundled as possible. Put three hats on your head if you can. i've slept in a beanie that was covered in a scarf that i covered with my jacket hood (I was sleeping outside in the colorado mountains during winter). it made a HUGE difference, and sometimes it makes all the difference, and LOOSE clothing, all the way. someone mentioned something about cotton being bad, and they're right. use animal fibers if you can (wool, fleece, etc), or synthetic stuff if you have access to it. If all you got is fruit o the loom, then keep your shit DRY and CLEAN, because clean holds more heat (the fibers are loose and available to trap and store heat when it's clean, and when it's dirty, they stick together and get bogged down, making less room to trap heat in)
4. SPACE BLANKETS. I always carry at least two heavy duty space blankets because the light flimsy ones tear way too easy, and that defeats the entire purpose of their function. use the space blankets INSIDE your sleeping bag, so you trap the heat made by your body against your body to keep your body warm... putting it on the outside of the sleeping bag doesn't do shit unless you're making a tent/wind break with it, which is usually why I carry two. the benefits of the heavy duty space blankets is that they not only don't tear as easy, but they trap in more heat, you can use them as a sleeping pad if you really need to, and they last forever. I had one that lasted for two years of regular use on the road and it was STILL going.
5. having clean clothes isn't always a top priority for dirty kids, but folks, clean clothes trap more heat than dirty clothes so if you can't wash them, pick the cleanest ones you got and sleep in those. all that grit and grime destroys the insulation properties of any fabric, which is shitty during the winter.
6. try and eat something before you go to bed. digestion makes the body warm...ever notice how when you eat too much in the summer, you get so hot you get sick? shitty in summer, awesome sauce in winter! eat something and drink a little something- though not so much that you will have to pee in the middle of the night and ruin all the heat you've been building-- just before bed. Just make sure you piss before you go to sleep.
that's all I got for now