SERVICE CHECKS - Winter time is a great time to get your fluid levels checked, to ensure your heating and cooling system is working properly, and to make sure your four wheel drive is in good working order. You can take your vehicle to the local service center or look in your owner's manual for the access points to your fluids and systems.
TIRES AND CHAINS - This is very crucial to preparing your car for snow. Even if you have to wait in line for several hours to get your car serviced with appropriate tires - it's worth it! Go to your local tire dealer and find out what they recommend for your vehicle. Often times snow tires can be very useful for weather beyond snow. One tire company will actually give you your money back on chains if you bring them back unused in Spring. Definitely a good investment in being well prepared.
WEIGHT - A few days before the big snow is set to arrive look into purchasing a few bags of sand or possibly use those old cinder blocks that have been laying around your yard. This is will weigh down your car and give you that much more traction on the road. Try to do this as close to the snow day as possible as more weight also equals less fuel economy.
FILL'ER UP! - Fuel is the number one supply to stock up on before the snow. Fill your tank at least half full before the storm hits. A full tank is even better. If power is knocked out you may not have access to re-filling your tank for days. If you are stuck in the snow somewhere and have to wait while some one comes to get you the extra fuel can keep your car idling for a while.
FOOD, BLANKETS, CLOTHES - It's also a good idea to keep emergency supplies in your car all the time but especially right before snow. Pack up a small bag of sweatpants, socks, blankets, and some extra food. Flashlights and other safety equipment will also prove useful. Hopefully you never have to use but if you need it - it will be there!