Hose it down! Spray down any concrete, stone, or brick areas with a garden hose to cool it off.
Rent tents. If there's no natural shade to be found, you can rent large tents to provide an escape from the sun.
Misters. You can get yourself an outdoor mist cooling system, hook it up to your garden hose, and set these fabulous misters up anywhere.
Frosty treats. Treat your guests to cool treats like popsicles