The two times I visited Colorado during the winter it was beautiful but COLD... yes water is very important to survival, but exposure to the elements can kill you more quickly than thirst. As others have suggested, I would plot out the materials and prepare the area for a temporary shelter before snow falls, just in case... but with my (lack of) experience in winter camping, I would have better luck staying close to a city near the BOL and sleeping in a truck with lots of blankets and camping gear, using other forms of shelter when available. It would have to be pretty darned apocalyptic for you to stand better odds of survival alone in the winter wilderness, with only a truck as shelter. You don't want to be this guy:
http://en.wikipedia.org/wiki/Christopher_McCandless
For living out of your car... I would recommend getting a small power inverter so that you have a means of powering a laptop, charging a cell phone, inflating an air mattress, etc. I still stand by my statement of being around some kind of civil infrastructure for as long as possible when living out of a vehicle, for three reasons:
1. Civil infrastructure is designed to accommodate people and vehicles; mother nature is not.
2. More potential shelter, aid, materials etc. available
3. Its the environment you have the most experience living in. If you don't already have experience living in the winter wilds, a crisis is not the time to start learning.
I don't mean to sound too opinionated; I'm not a survivalist veteran or anything. I just try to keep realistic expectations of what I am really capable of in a crisis. I have received a lot of inspiration on this forum, but some of my measures that looked good on paper were revised heavily when I actually tested them in the field.
Good luck in your endeavors!