Hands & feet get cold when your core temp is challenged and your body reduces circulation to the extremities. Remember, 100% of your blood flows thru the kidneys. I sewed two small pockets at the kidneys on my thermals and place handwarmers in there. Hardly ever been cold or experienced cold fingers or toes. One warning - you need to have a T-shirt or some other layer under the thermals (or use thermals as base layer and put T-shirt with pockets over top) to avoid 2nd degree blister burns. Yes, first time it did get that hot!
Another consideration is whether you're in a ground blind or treestand. As others have suggested, blanket/carpet/overboots/etc as a thermal break against ground are very effective at stunting the cold conduction path. Being in treestand is bit more challenging, but I place two thick carpet squares on platform (do NOT leave them out, or they may get rain/snow/sleet soaked) which also help combat wind chill.
How do you keep your feet warm?
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