1. Make sure you eat enough. You need more calories when your body has to work to keep warm. And even more if you’re trying to move through heavy snow, and heaps if you’re shivering.
2. Eat carbs. Your body prefers to burn more carbs in the cold, so make this your primary source of fuel.
3. Drink (even when you don’t feel thirsty)! You surprisingly lose more fluid than you expect, since cold air has less water than warmer air, and cold temperatures dull the desire to drink and pee.