If your feet are cold, put on a hat. In fact, while sleeping, a great way to keep your feet warm is to sleep with a sherpa had or similar type of head covering. You lose a lot of your body heat through your head.
If your feet are still cold, try these tips.
1. Change your socks.
2. Take your boots off and rub your feet.
3. Put on vapor barrier socks. You can use baggies for this.
4. Wiggle your toes.
5. Get off the snow and insulate your feet from the snow. How?
Stand on a rock.
Stand on some branches or pine needles,
Stand on an insulation pad. Theses are lite and can be carried in your pack.
These can all help. But remember to carry mole skin. This will help repair and protect your feet while traveling.
Just remember to wear a hat. That is the best way to keep your feet warm.