Tree shade is good. Marquee shade is not. They trap the heat.

Another thing I did one very hot year at Woodford Festival, where every day was 100 or more, was get one of those cloth hats that has the bit hanging down the back, put it in a sink or bowl full of cold water so that it was completely saturated, then stick it on my head. The cool on my neck was great. As it dried out, I would go and wet it again.