what works for me...I'm very susuptable (sp) to heat because of my meds, health issues, and just plain being half Yankee
I wear a cooling vest and prefer the fabric kind under my Tourmaster Sonora mesh jacket over a coolmax long sleeve shirt
I can't recommend more the covering of the arms to prevent the wind from heating one's skin up
On Run for the Wall west and mid west scorching temps, they had an ice chest with ice/water, and those crystal cooling neck bandanas floating in there in between stops...those are great for keeping one cool as they are against the neck blood vessels.
Packing for me: my right side bag is my tools, maintenance items, and fix it stuff along with spare quart of oil and filter.
I have a Nelson Rigg weekender seat bag which is my luggage with clothes and personal items in a garbage bag which is my take away from the bike luggage !!!
I bring 4 or 5 bottles of water in my trunk along with a small, hard inside ice chest from WalMart for $6 (sized for 6 pack canned drinks) which is my food items.
I put in there a ice pack in the bottom with a turkey sandwhich or two, and bananas and necterines or lately I favor plums.
Cold fruit is quite refreshing and a lite snack. I'm diabetic and must have food with me at all times for snacks all through the day.
There are a couple packs of peanut butter crackers in the tank bag and handy.
When I'm overheated or just hot, I find I can't eat anything heavy and not at least cool.
In my left side bag, is a WalMart thin and curved insulated water bottle full of ice water. I use that to water down my cooling vest when a sink is not available or just to pour lotsa of ice water on myself. I also have another WalMart $6 (sized for 6 pack canned drinks) chest with 4 1 liter bottles of frozen water and a couple of canned drinks on top. Then I have kept 20oz drink bottles and they are filled with frozen water and just put in the side bag so they melt as the day goes on. I also put a few other 1 liter frozen water in there.
I have three bottle holders...a middle main cup holder, and two "hook on the tank bag" neoprene items, so in front of me are three bottles of water.
Two just water and the middle is a 20oz bottle of frozen. I can drink some ice water, or pour ice water on me on the fly, and then take one of the other water bottles and pour it in the iced middle bottle as a refill. I constantly sip ice water and pour a lot of it on my refreshing the vest and cooling me off on the fly.
If it's really hot on the slab and well over 100 heat index, I pour enough ice water so some ends up in the front of my mesh pants which really cools with a shiver.
regardless, I've had to stop after 200 miles in July when seeing double and my thinking starts going to mush. I realize I have to head for a Wendys, etc purchasing a large soft drink, and lay on a booth bench under an air conditioner vent for 30 minutes.
hope this helps and much luck and karma your way on your trip...I wish you had proper summer gear with for me is big holes mesh like my Tourmaster gear.
(I found my old First Gear stuff was greatly more tighly woven and less air got through)
lastly, because of my great amount of lighting including my Clearwater Kristas and Glendas and rear hyperlites, I'm much much more comfortable riding in the middle of the night on the interstate. So I do favor riding between sunrise and noon, but will ride in the dark with cooler temps, no cops, and little traffic except for the big trucks droning along in the right lane. I stay in the left lane and set my cruise to GPS 79mph. I am vigalent mainly for debris like retreads in the road. Have never seen deer or critters (knock on wood) while riding the interstate east of the MS mostly from LA to TN.
ride safe and be careful out there,
Mike in Nawlins'