I haven't had time to read through all the replies, but since I'm from the Chicago area I'll throw in tips on what I do to keep prepared for the winter commuting.(Even though we have had an unseasonable warm winter this year I still stay prepared.) Hope these ideas help!
1. For your car: go to a car store or walmart and buy a couple bottles of "Heet" (no joke). Put it in before you fill up your gas tank. It helps to keep your fuel-lines clean and prevent them from freezing in super cold weather. I usually do this if I know a cold snap is coming.
2. I have a small car and keep a large jug of cheap kitty litter in the trunk. If I get stuck in snow/mud I pour the litter around my front tires (front wheel drive) to create traction. The litter clumps from the moisture. Also the extra weight in my trunk helps in snowy weather. Containers of sand would probably work as well.
3. I keep a back-pack with extra polar fleece jackets, socks, flashlight, partially filled water bottles (if they freeze the water needs room to expand), granola bars, matches and a small candle. I also always have at least two blankets.
4. I keep a shovel in my car trunk as well. (they make them with extendable handles - walmart)
5. I've bought a black and decker rechargable battery jumper. Way better than jumper cables, and you can also plug a cell phone charger into it in case of emergency. Great to have year-round.
6. Keep a small first aid kit in your winter back-pack car stash (they are cheap and often come with glow sticks and those foil-looking mylar blankets that keep body warmth in - I actually kept one of these from a marathon i ran so that i have an extra. Plus they fold up really small.)
7. My number one tip as far as driving goes. If you go into a skid on snow try not to panic and slam on your breaks. Steer into the slide, use your breaks gently to prevent further loss of control. Best thing to do is lay off your gas/accelerator, steer carefully, and ride it out if you have room on the road to do so.