what should i wear to a...

Are you camping? If you are bring clothes you don’t really care about because it’s quite possible you’ll lose them or they’ll be stolen.
I find shorts and tights good, because you can sit down on the ground without worrying about flashing people and it’s less warm than jeans. Tights are a good idea because they stop your legs from burning and keeps them clean. Keep your self covered up well if it’s sunny, getting sunburned will ruin your fun. I’d advise wearing a lightweight scarf, you can wrap it around your head to keep the sun/rain off.

Go second hand/cheap store shopping and find some nice, cheap clothes to bring with you.

Wear a long flowy dress with flip flops. That way if its really hot your clothes wont stick to you and it will be nice and breezy. And if its a little chilly you could just throw on a wrap (love quotes!) or a cropped jacket.

^If you wear flip-flops stay keep to the back of the stages or your toes will get trampled on.