“A human’s greatest protection against the cold is the intellect.” To be warm:
Exert yourself physically. Exercise, sport, heavy lifting, something.
Insulation is what most people think of. They wrap themselves in plenty or go in a house.
Food and beverage, well chosen, will give you carbohydrates, starches, fats, and water, all of which your body will use up when it’s cold. Even if you’re losing weight, the cold demands more of them, so it balances out. They can give you vitamins and minerals, which help keep your body in good condition.
Resting well, not just relaxing but falling asleep, helps repair the lttle bits of damage your body took while you were awake. That repair means your body has an easier time staying warm.
Exertion circulates blood. Blood is warm and it’s mainly how organs stay warm.