Many people scare you with the thought of there being no showers at festivals, which is actually completely untrue, it's just knowing where to go. Every major festival will have public showers and if you get there at the right time they can be rather pleasant.
Dry shampoo is a good option if you want to wear your hair down because it absorbs excess oil. If you're glued to your hair straighteners, some festivals actually have hair-straightening tents.
Get into a good skincare regime in the run up to a festival and one that you can continue when you arrive. It's best to keep your make up light and simple for a festival, and avoid heavy make up that you can't remove without the wipes or remover you'll be taking with you. If you want to add a bit of colour, some lipstick, eye shadow or liner will work a treat. Suggested make up for festivals include concealer, SPF foundation, eye brightener, eyeliner, mascara and lip balm.