Snowboard clothing is a matter of proper layering, so start with the layer closest to your body. On cold days, wear a base layer of sweat-wicking fabric, like Icebreaker's Bodyfit line, which breathes well, feels good against your skin, and transfers sweat away from your body. Avoid cotton, which absorbs moisture and will leave you damp and uncomfortable all day.
On colder days, an insulation layer is an imperative. Insulation does just what it says--it keeps you warm. Long-sleeve shirts, pullovers and fleece will work for an insulating layer. Remember, you're going to be active, so make sure that you wear something that's easily removable if you get too hot.
For your outer layer, water resistance is the key. Your jackets may vary, depending on the weather, but since you'll be spending a lot of time sitting on the snow, make sure to find the highest level of waterproofing for your pants. To stay comfortable on warmer days, look for pants with breathable fabric or vents in addition to water resistance. Burton's 2L Gore-Tex snowboard pants are waterproof, vented and breathable.
Don't forget a hat that covers your ears and warm, sweat-wicking socks. Also, make sure that your gloves are waterproof and well-insulated. A good pair of goggles is important as well, since the sun's glare will be magnified by its reflection from the snow. Try Zeal Optic's polarized line of goggles.
Boots, Board and Bindings
Your boots, board and bindings are what will ultimately make or break your day. Make sure your board is the right size for you, and that your boots fit properly to keep you comfortable on the hill. If you are buying your board, boots and bindings, make sure to get them at an outdoor sports shop, where a professional can make sure that your gear fits your size and experience level.