Great advice about not getting over-heated on the way to your hunting, or during your hunting.
Superb boots and a great hat are a must. When it gets really cold I switch to my old wool pac boots. Those, with wool sox with polypropylene liners, and poly glove liners too ...Thats the ticket. A neck gaiter, a hood if needed. Some chemical handwarmers .... a few snacks that can provide you calories right away (candy bar or an apples, a banana) and make sure you're hydrated. Eating anything more than a small amount can rob your extremities of warm blood as digestion can cause your "core" to demand more blood and warmth for the process. So little snacks regularly are the way to go.
Don't sit down on something wet and try to keep yourself and your feet out of low holes with water or ice in them.
It's amazing how when hutning or ice fishing just keeping your feet on a 2 X 4 or a 2 X 6 can make such a difference.