I wear thin t-shirts and shorts in the summer. I hydrate as needed, and if I'm sweating a lot I will make a gallon of lemon-ade, orange-ade, Grapefruit-ade and add 1/4 tsp kosher salt (no iodine added) to the mix to keep salts up. I have single sized coke bottles (plastic) I fill them half full of my fruit ade mix and freeze them overnight. This way I can fill the rest of the way with more fruit-ade and have cold fluid.
If I have a long day ahead of me, I fill the bottle leaving 2-3 inches at the top - which is about 2/3rd full. I do not add any fluid to them, and let them defrost in my carry-size insulated 'pack' - or purse.... Its technically an insulated lunch box.
If you get overheated, use alcohol swaps or a papertowel with a bit of rubbing alcohol on it and wipe the soles of your feet and palms of your hands - alcohol evaporates faster and more in humid conditions, thus you get the cooling effect. The feet are your primary radiators, thus cooling them off makes you feel cool. So soaking your feet in a swimming pool makes you feel so much cooler.
If you are feeling flush/overheated in the face, then wipe your forehead and the back of your neck as well.
I have a pair of leather sandals - sort of like these:
They have enough sides for support, but are open enough to allow the feet to breathe - as long as you don't wear socks, you can stay relatively cooler just by wearing sandals.
If you do not have an air-conditioner, but do have a fan, take a pillow case or a bit of and old sheet (100% cotton is best) and cut it or fold it to fit over the front of the fan part to allow 50% of the air to continue to flow. Get it damp not dripping wet, but wet enough to where if you press it a few drops of water come out.
This will give temporary cooling of the fan. The higher the humidity the less cooling you get.
One of the mistakes people make with heat waves, is they keep their windows open 24/7. The ideal way to do whole house cooling is to open all the windows and doors and put 1-2 fans at a window pointing outward to exhaust air out of the house at night. Early in the morning before the heat starts up, or mid-day, close all the windows to keep the house relatively cooler with the trapped cooler night air.
Keep an eye on the temperature. If its 100F outside and the inside temperature goes above 90F, then you need to open two windows across the room, put a fan in one window blowing out, and one at the other blowing in. Use a damp cloth on the one blowing in to help cool the room.
Another method is to hand a sheet in front of one open window and spray it with a mister to get it damp with a fan in another window opposite if possible blowing outward. Air comes in through the window with the sheet on it and cools off a bit while evaporating the water. spray to keep the sheet damp.
Make 'ice packs' I use gallon sized ziplock bags, I put in about 3/4 cup of liquid dish soap, seal the bag to keep it from leaking and lay it in the freezer. The dish soap will into freeze solid, but it will lose its transparency.
Once the bag is 'frozen', wrap in a tea towel that has been wetted and wrung out, then lay that across the back of your neck/shoulders - it will help cool you.
The wet towel will slow down the heat transfer between your body and the ice pack, and will spread the cool more even out and will evaporate a little to add to the over all length of time off cooling.
If you have a small insulated lunch box, you can carry 2 icepacks in that and have them handy if you are in the bus or something.
Or hold in the the palm of your hand, or place against the soles of your feet. Depending on where you are and if you can get away with it.
Now I never tried it, but there are now these 'gel' insoles which (in theory, I never tried it) be put into the freezer and the get gets super cold but doesn't harden - slip into the shoes before you leave to help keep your feet cool. I suspect it won't last long.
Yeah it looks silly to put an icepack on the back of your neck at the bank - but you can either look silly or be more comfortable.
BTW, yes you can use the liquid dish soap after freezing and thawing over and over again.
15- minutes before bed - I use a spray bottle and spray plain water over the bottom sheet of my bed - getting the bed just a touch damp. The water evaporating will cool the sheets even more. I even keep a spray bottle of water near the bed set on misting, which If I wake up when its too hot I spray the mist upward and get a 'rain' of mist which helps keep me cool.