(this is a bit long-winded with a lot of numbers. my apologies if it's too much to read, but there is a tl;dr at the bottom)
I'm a rookie myself (less than two years driving) so please don't take this as condescending. This is my second summer and I've suffered heat exhaustion twice in the past three weeks. The first time I was pulled from the route and had about a week off to replenish/recover. Felt fine after a week, went back to work, made it three days before it happened again (I finished the route that day but had to call out the next.) So I let my team know, went to get bloodwork done to figure out what I'm missing, and next thing you know the doctor's saying I need an ambulance to transport me to an ER due to extremely low sodium content.
I drink 10-14 16oz bottles of water a day, at least 56oz of sugar-free Gatorade, and I keep a liter of Pedialyte in my cooler at all times to sip on as needed. Where I've been lacking is my diet, so I also take 3 supplements a day: magnesium, potassium gluconate, and dicalcium phosphate. Thing is, dealing with heat indexes of 100F-115F (about 80% humidity), it just wasn't enough.
This job is absolutely easy in a sense. You follow the methods, deliver the boxes, get the job done. Dealing with the elements can be a dance with the devil, though, and in these hot summer months you really need to take care of yourselves and be aware of any negative changes in your body/the way you're feeling so that you don't end up in the same position I've come to find myself in.
Proper hydration isn't just about slamming fluids and taking your lunch break when you're sweating for 10-12hrs in this summer heat. You've got to ensure that your diet is also providing you with more than just energy and a feeling of fullness, even when taking supplemental minerals and electrolytes. You can't let yourself get stuck in the back of the truck looking for that one package that you were just told was scanned and loaded on-car. Keep an eye out for shady areas when pulling up to a delivery location-- even if you've gotta walk an extra 20ft, do what you can to park out of direct sunlight and make sure to occasionally open the bulkhead and backdoors to let some of that oven-worthy heat escape back out into the wild. Make mental notes of places where you could take a break in an air-conditioned environment, and for Christ's sake use them to cool down and prevent yourself from starting to develop any kind of heat illness.
I know they pound this stuff into us at PCMs, and I also know that once you're on-car you may just want to get the day over with as quickly as you can (especially the newer drivers.) It's easy to tell yourself you just need to weather the storm for one more hour, or you'll get that next bottle of water after your next stop, or you'll wait until you're in a certain area to take all or part of your lunch break. Don't do that. When the thought first hits you that you need water, get water. Same with food, finding a place to cool-down, all of that. Don't postpone it and, if anything, try to make it a habit to take action before you have those thoughts.
I hope everybody stays safe and healthy out there because, depending on where you work, that can be much easier said than done.
tl;dr: Don't be dumb. Take care of yourself during these summer months.
*edited a few times to make for a cleaner read. I always proofread after I hit post, lol. Like an idiot