Thanks everybody for all the great responses. I'm gonna add some salt and sawdust/sand to what I carry in my trunk. Something I got in the habbit of carrying with me last winter was a Coughlan's Solid fuel stove. I figure if worse comes to worse, it's not a bad way of getting a fire started, and could make an extended stay in the car a bit more bearable (with proper ventilation of course). another thing that can be of help is some good rope or a length of cable or chain....a few years ago (as I recall, it was my first excursion into serious winter driving), I got spun around and ended up in a grassy median. I had no traction. A guy in a Jeep drove by and stopped. He had some rope and he pulled me out. One of those things like jumper cables...you can't count on someone else having it.

-Chris