x2 for the balaclava... lifesaver, especially if windy (doesn't negate need for Chapstick though).
Tent... there's three and four season tents. You need a four season if you expect it to be set up
while it's snowing, and will be under a heavy load. If not then a three season tent will do just fine.
Don't rule out making a snow shelter. It takes some time, but is a worthwhile experience to have. Read up on it first; I've done it twice and really enjoyed it. You'll sweat, sweat, sweat while building it, so the extra clothes/socks mentioned above really will come into their own if you're going this route.
Little avalanche shovel - this is a must if you're in the mountains, as would be avalanche probes/walking sticks, and a beacon for each member of your party. The shovels are only suggested (not necess') if you're in the flats, but do make quick work of moving snow, like if you were setting up camp for a while and wanted to set your tent on a more flatter/sunken surface, while berming the excavated snow to face the wind.
More matches than you think you'll need. Inability to light a fire is a trip-ender in the winter, as opposed to just a bummer in the summer. haha.
Yeah, skip the alcohol consumption if it's going to be real cold. Better walking out healthy and warm than waking up hungover (you're gonna need more water to rehydrate anyhow, which is just more work) or carried out hypothermic.
First aid kit. Essential.
Cell phone? Recommended. Getting into trouble in the woods is far more serious when 12 feet of snow hampers your attempt to return to where you parked. If you injure yourself, being able to call 911 would kick ass over having to hump it out.
Unless you're certain you can keep your bag dry, don't use a down bag... go synthetic, and go for one rated for considerably colder than what you're expecting. Being cold sucks ass. Hard. In fact, keeping your bag dry is just good, day-to-day advice.
Camera. You're gonna want pictures, for sure.
There's way more, I'm sure. Have fun, lucky bugger.
Nearly forgot... Purists may like to use birch bark toilet paper and cook over a fire. While both sound like fun, I'd highly recommend planning on cooking everything over a backpacking stove and not over a fire. If you wind up using the fire; great, but you really should have a small stove. You can go butane/propane if you want simplicity and extra weight, but I'd suggest white gas for hotter/quicker cook times and lighter weight fuel and gear. A look at any outdoor supplier will net you good results. I've had an MSR Whisperlite for over a decade, adn it rocks. DON'T cook inside your tent. You'll asphyxiate on carbon monoxide.