My feet seldom get cold, but I do have some experience sitting in extreme cold. Some tricks, knee-length wool socks, I use German military and wear two pairs. Even moist wool will keep you warm. I've tried many many high tech socks and always go back to wool. Some parts of your body radiate more than others, your calves, your center, your neck, and your head. If you keep these spots warm the other parts of your body have a lot easier time staying warm. You can heat your kidneys and warm your whole body. I unlace or loosen my boots when sitting, seems to work out better for me. I also wear my boots slightly loose, half-size too large. Wearing my Meindl Island (Iceland) my feet seldom get even a little cold. I had a really old school pair of Wellington style zipper boots with real Lamb fur inners, the only part of my foot that ever got cold was the sole when sitting, a pad to stand on fixed that. My Zipper boots were also half a size big.
I sometimes sit in a light sleeping bag or my favorite is two military blankets sewn on one side and the bottom, easy to get in and out, they seem to breathe better than a sleeping bag and still keep me warm when moist, they are also quiet.
The last trick, eat a good meal before you go out, stoking the furnace helps. Carbohydrates for the short boost, protein for the long hall. Beef and Beans or Fish and Taters.
I use wool gloves and keep my hands mostly in my pockets. In extreme cold, I have a couple of warmers in my jacket pockets.