It takes quite a bit more muscle to spring from turn to turn and in doing do so, you lose a lot of fluids due to sweat. Not to mention how difficult it can be digging yourself up from a tumble. To battle the muscle fatigue, eat small carbohydrate loaded snacks frequently throughout your day. Try nutrition bars, bananas or even a bagel stuffed in your jacket to nibble on. Junk food will do nothing for you.
Apples are fantastic because they provide hydration in addition to carbohydrates and natural sugar.
OK, now you have had a quick refresher on how to nourish and hydrate your body, you need not to forget to stretch. Oh boy will you feel your legs and back after a strong powder day. Your basic leg and back stretches will suffice. Do them immediately after your last run of the day. You will get more from them and you will not stiffen up as easily after sitting for an hour performing the Apr s-ski thing.