OK SO! As an 8th generation Texan, I have some experience with heat that Can And Will Kill You.
That said, I've been getting a lot of questions from friends asking for advice on dealing with this bullshit, especially if you're somewhere where air-conditioning isn't widely available.
1. Electrolytes. Everyone tells you to hydrate, but if you're sweating balls and flushing yourself out with fluid, you're not just losing water, you're losing salt. You don't need to buy those fancy liquid IV packs if you don't want to; I literally just dump a little pack of salt in my water bottle every now and then because I stole a shit ton of them from my school's café last semester because they were free. This is to keep yourself from passing out. Sports drinks or salty foods work too.
2. Get yourself a fan. Any sort of handheld thing that can blow air on you. Don't use your own hand as a fan because you'll exert more energy than it's worth.
3. If you are immediately feeling hot, you are going to try and get ice, a damp cloth, or something vaguely cool, and you are going to press it to the inside of your wrists, the back of your neck, and behind/under your ears. The veins/arteries are really close to the skin here which I believe is most of why this works so well for cooling you down.
4. Pressure points aside, just pour water on yourself. If you need to regulate your body temp, do so. No one is judging you, I promise.
5. SUNSCREEN PLEASE FOR THE LOVE OF GOD THE SUN IS A DEADLY LAZY
6. Get yourself a UV / SPF shirt. Something lightweight that will shield you, in a material that will cool you down. You can also get it all the way wet and then wear it, if that's viable for you. You won't be walking around dripping—it'll just cool you down significantly.
7. I've seen some people talk about putting clothes, especially things like socks, underwear, and hijabs into the freezer overnight? Have never done this personally but fair enough. Same principle as above.
8. If you feel yourself getting hot, say something early. Heat stroke is no joke. "A cold baby dies, a hot baby dies" applies to adults too.
9. If it's dry heat, stay in the shade. If it's the humidity getting you, godspeed.
10. Don't open the windows when it's hot. This is a trap. You think the air flow will help. But the air is hot and not your friend. Windows stay closed unless you specifically want the outside air coming in.
That's all I can think of right now off the top of my head but feel free to add more!