Every year, the Centers for Disease Control publishes their list of items drivers should have in their cars.
Among the items are: cell phone with charger and extra batteries, shovel, windshield scraper, radio and flashlight with extra batteries, water, food, and blankets.
The entire list is available from the CDC and people can buy kits with many of the items on the list for $50 or $60. It's a good idea for you to add a snack of your choice (granola bars work great) and pet food if you travel with them.
The list is fairly standard, but what would you add to your emergency kit in case you get stuck in the snow?