If you live in, or expect to drive through, an area that suffers from winter weather (including freezing temperatures, snow and ice), the Colorado Department of Transportation suggests your emergency kit should include these items:

First aid kit
Essential medications
Flares or reflectors to signal for help and warn other drivers
Flashlight
Extra batteries
Jumper cables
Snow and ice scraper
Snow brush
Survival blanket or sleeping bag
Tire chains and/or tow straps
Extra set of winter clothes
Snow shovel
Non-clumping kitty litter or sand for traction