I also raced motorcycles (dirt) & bicycles (everything) so that involved a lot of activity in heat (& cold)
I heavily agree with Jamie. Even down to the bananas.* The physiology as I understand it is when you sweat your electrolytes get depleted of water, making them thicker, then you become sluggish. You sweat out more water by percentage then any part of the electrolyte. It is just electrical resistance. Of course I could be wrong on this. Once you start working out daily and ‘get used to’ sweating you will find your sweat won’t be as salty. Plain water will get back in you system quicker than anything. Electrolyte drinks are more for after or before, not as much for during.
I find what you do the day before is OK but the 3 days before will make more of a difference. So start hydrating sooner and think long term. Same for food and sleep.
Any cooling where you can feel a pulse is pretty effective. Wrist, neck etc.
In karting I think we can get a little distracted as to how much effort we expended. I found in running or weightlifting it is obvious because it is boring. Something like dodgeball is way more fun and just doesn’t seem like a workout even though it is. Chasing a ball is enough to take you mind off of the work.
*I was eating bananas for the heat. I had a single kart accident and went off pretzelling a spindle and tie rod. Somebody asked if I found the bananas made a difference. I told them I don’t know about the heat but it sure seem to give me monkey grip on the wheel during the crash. What has helped me on grip is working on my grip, Learning how not to need grip and not cramping up. I feel my arm strength helped me in the crash.