Step 1... ( Warm Weather ) Lots of cool water, I keep mine in a big styrofoam cup in the cup holder(if you have on in your truck) take a sip every stop. Dont chug
Step 2... ( Hot Weather) Get a decent sized ice chest. Something that can hold at least a bag of ice, but something easy enough to carry around.
Step 3... (Really Hot Weather) Place a hand towel or something similar in ice chest and make sure its soaked, wrap around you neck, every 20-30mins, resoak in ice water. Dont be afriad to get a little wet, makes a huge difference
Step 4...(Hell) Use above 3 steps and I add a clip on fan I bough from amazon, keeps the air moving and plugs into a 12v car adapter(do this at your own risk).
If I do all those things the heat never bothers me, its just a pain to have to set it all up in the morning.