Even though it's Winter, if you're getting out and active in the snow you still need to drink water. Since you are already loaded down with gear like poles, a regular water bottle is way too bulky, and plus it might freeze.
That is why this StoAway ($35) by Camelbak is great. The super durable plastic bag inside that holds 70 ounces of water, and the external circular purple cap makes it easy to refill. Since it's so slim, it can fit inside your existing backpack with all your other necessities. The drinking tube allows you to access your water easily, so you're more likely to drink it and stay hydrated. All you do is bite the end and suck out the water just like a straw. The bag, tube and bite valve are all insulated, which prevents your water from turning to ice. The StoAway is not just for Winter; it keep your water cool in the Summer. Sounds like a good deal to me.