Packing your car with the proper supplies is probably the most important thing you can do to avoid getting stuck on the passes. Having reflective triangles, flares, and lights to identify your car on the side of the road is an important thing to have.
If you are stopped because of the snow, it is important to have chains, gloves, and something to kneel down on while putting them on. Water-proof gear is also important to keep you dry.
You should also have jumper cables and a tow rope inside your car. If you are stopped for long you will need warm clothes, a blanket, and sleeping bags to keep warm.
It is also good to have some food and water with you keep your energy up.
Probably, the most important thing to have is a fully-charged cell phone. That way you can call 511 for road conditions, for AAA, or for family that are waiting for you. Before you get out on the road, make sure you are ready for anything.