Umbrellas

What's the most popular way to keep drivers and riders cool while they are waiting at the Start Line?
An umbrella!
Go out and chuck some in the trailer now!

Also consider buying or making your very own cool suit, there's plenty of ideas on the web.

Please remember it's your responsibility to provide your own protection. Think about how you can keep cool now. Bring plenty of shade and water. There will be plenty of ice for sale. Sun screen, sun glasses, hats, fans. If your in a car check out those trucker fans bolted to your dash. And if your riding a bike, don't walk around with your suit zipped up all day, I can guarantee you will fall over.
(These photos were from Speed Week 2018)