Bobert, are you going to be on a stage with stage lights? That can be a real killer in the heat - especially if it's in a marquee. Those things hold the heat in. The only relief I've had in those circumstances was at one festival when they got a big fan and directed it towards us. Wear as cool clothes as you can manage - preferably light colours (dark colours absorb heat).

As Sandra said, it's important to drink lots of water - also those drinks with electrolytes in them. If you are going to be in the sun, then a large hat and sunscreen is essential.

I can imagine being one of those dancers in the heat. When you have to wear costumes in inappropriate weather, it's tough. I had some experience of that at Snalbans festival (which wasn't even in summer, although it was a warm day). John and I joined in with Wayward and, of course, to look the part, we had to wear the medieval costumes, march up the road banging drums, and perform on a hot stage in a marquee under stage lights. It was fun from one point of view, but boy was it hot!