You loose a lot of heat through your head. So, remember to wear some type of hat or beanie to cover your head and ears. A neckwarmer is a good idea also. Also, wear goggles to protect your eyes. Goggles will keep the wind out of your eyes, and protect your eyes from the glare of the snow.
Sunglasses offer little protection while snowboarding.
Sunglasses fall off easily, and fog up. Also, goggles will protect your face better when you fall than sunglasses will. A good pair of socks is also important. It is best to wear snowboard specific socks. Snowboard specific socks are made so that the sock does not bunch up over your instep.