I too use a 2 liter source and a nalgene bottle. The nalgene bottle is kept in my sleeping bag overnight and is my initial water supply. It hopefully lasts until my backpack source thaws out. I've yet to find a better system during cold weather hunts in CO.
I carry a 2L platapus hoser bladder and then a 1L Platapus soft bottle for mixing energy drink. I use the 2L Playtapus gravity feed water filter system, so if I stop for lunch near water it makes it really easy to fill up, and just use the water directly out of the filter bag to make my meals.
If push comes to shove, I have the ability to carry 5L of water between the 2L dirty bladder, 2L hydration bladder, and 1L softbottle.
3L Platapus Big Zip in pack. Two Sobe bottles of the Citrus Energy on the sides of pack. After those are empty I use them for my W.A. energy mix. Have a 10L Dromadary bag that I still have yet to use due to finding H2O seemingly every where I go. But I am sure it will get its use soon enough.