Two words: Merino Wool. You should leave your tent in the morning shivering your *** off, as you will quickly warm up with a Merino base layer. Also, when you start to get hot, the Merino will not be as bad as poly or cotton for overheating. I find that a medium Merino base layer and even a light pant and jacket is plenty down into subfreezing weather, once you get moving. Similarly, you can handle some moderately warm weather for a while, and just peel off your baselayer and shove it in your pack when it warms up. Backpack hunting sounds like fun, but there are a lot of uncomfortable times (getting up in the middle of the night in subfreezing weather to pee isn't all its cracked up to be). Thank heavens we are so lucky to get to experience this.