My winter traveling kit has the following:
1- Mountain Hardware Zero Degree Sleeping bags, synthetic insulation - I keep the sleeping bag in its storage bag (vs. the stuff sack).
1-Mountan Hardware Bivy Sack
1-Therma-rest CAMPREST pad.
2- Fleece Sleeping Bags

I prefer the sleeping bag/bivy combination because it provides basic shelter as well as insulation. The Pad is very important because it provide a huge amount of insulation where you need it most... beneath you (two thirds of your insulation should be beneath you to keep the ground from sucking warmth from you).

The Fleece sleeping bags were cheap ($10.00) and work well as a blanket. I added those to my kit for other’s if the need arises and more as a snivel item vs. a survival item.

Another relatively cheap option are woobies (AKA poncho liners) I have a couple poncho liner with zippers added to increase their versatility. They are not ideal for sub-freezing temperatures, but are usable and a good replacement for blankets. I have one in my kit for warmer weather use, along with a dirt cheap www.countycomm.com sleeping bag and a military poncho. Lots of uses in a small cheap package.