Two products I'm using are really helping to make summer heat easier to handle.
For this first product I need to say that baseball caps are poorly designed for summer hats. They leave your ears and neck exposed to direct sun. Top of ears, one of the most common places for skin cancer to start, because the skin is thin and aimed right up at the sun. Baseball caps make your ears stick out even further. Baseball caps may be responsible for hundreds of thousands of cases of skin cancer.
The first or these two products fixes that. It's called the "SunFlap", and it is found here: http://www.sunflap.com/
I found that it works as advertised, it's easy to put in or take out of your cap, and it stays in place even in high winds. It blocks the sun from your ears, the side and back of your head, and your neck. It's so light weight and comfortable you forget it's there. I occasionally dip my hat and the SunFlap into the river and put it back on for extra cooling. This goes a long long way to making a baseball cap a good summer hat. They start at $14.99. If you're going to wear a baseball cap, seriously consider getting one of these to make it a better summer hat.
The second item is a small portable water filter. I spend a lot of hours out in the river, water to my waist and sun beating down on me from waist up. I used to carry a bottle of water in the back of my fishing vest. There it would get hot from my body heat and the sun beating down on it. It was a nuisance to carry because of it's sloshing weight, and just plain hot to drink after a couple of hours. To get to the bottle of water I had to remove my vest, which meant I had to put my rod down, which meant I had to wade all the way to the bank...it was anything but convenient.
I purchased a "Sawyer Mini Water Filtration System". It's small enough to easily fit in one of the pockets on my fishing vest, and very light. It comes with a squeeze pouch and a straw. I tried the pouch first but it is so stiff I could barely get any water into it. I tried the straw next and it was so much simpler that I'll be throwing the pouch away.
This filter blocks out the biological bugs that can make you sick. It does not block out dissolved solids, so if the water is salty, the salt goes through the filter. The filtered water will taste the same as the water would unfiltered. But if the water tastes reasonably decent to begin with, then no problem. If it is skunk water then it's probably still going to taste like skunk water, even if it doesn't make you sick.
It doesn't take much suction to get water flowing through the filter, and it's cool water in summer, cold in winter. I like this gizmo and will be carrying it all the time now. I stay hydrated better than when I was carrying bottled water around. Price starts at $15.00 and you can find it here: https://www.amazon.com/Sawyer-Products-SP128-Filtration-System/dp/B00FA2RLX2/ref=sr_1_1?s=sporting-goods&ie=UTF8&qid=1468847142&sr=1-1&keywords=sawyer+mini+water+filter