http://www.outdoorresearch.com/en/accessories/storage-systems/backpack-accessories/water-bottle-parka-2.html
Plus hot water/hot drink, keeps warm all day when full. the problem is when you drink 80% of the water and let cold air in, then stick it in your pack, the remaining liquid can turn to ice.
but two of these are enough for ~16 hour trip at -20c.