In California, if Fish and Game catch you drinking with guns on public land, it's really bad. I could find specific laws if you want. No guarantee as to other states though...I do live in CA :-/. I've been told, however, that it has nothing to do with your BAC, your "I swear, it was just for the end of the day!" stories, etc. Just that you have alcohol with you.
On private land, you can do whatever you want assuming you don't violate any other laws and the owner is okay with it, as far as I'm aware.
Also, just a note, from a bio major and EMT-2: Drinking to stay warm is a TERRIBLE idea. It's been mentioned here before, but the reason alcohol warms you up is by constricting your blood vessels. Frostbite happens a lot faster when you're drunk because it's harder for your body to push blood to the extremities.
Use the pocket space for those chemical hand warmer packets. $0.99 for two of them at my local REI and they stay good for hours. Drop them in your gloves or pockets or just make a fist around them, or tape them to the top of your socks (always worked for me when I went snow camping in the sierras). Just my $0.02.