Commenter Jane *is* the pony made a couple of really important points that I thought needed to be really highlighted;
Another tip is to go outside (but under trees!) near a large body of water (lakes, reservoirs, seas). The heat difference between water and land creates a nice cooling breeze.
And don’t leave any living thing in a car!
Trees can cool the temperature around them by a really perceptible amount, because of the shade and also for the same reason that bodies of water do; evaporative cooling.
DON’T LEAVE A LIVING THING IN A CAR! Every year, children and pets in North America die, and die very quickly from heat stroke if left in cars; the temperature in a car skyrockets in a very short time. Cracking the windows does almost nothing. If you do nothing else, pass this along to everyone you know.
Also, if you live in the top floor of an apartment building with a flat, black tar roof above you, it is going to get very, very bad; the roof will absorb the heat and it will be radiated down into the apartment below. Consider relocating for the duration, if you can; bunk with friends or family someplace else. Once again, check on elderly family and neighbours who are living in this situation; they are very much at risk.
ETA; someone has just mentioned using a dehumidifier; I wouldn’t bother, because although they do pull moisture out of the air, they also kick out a significant amount of waste heat, which you really don’t want. Humidity makes if feel hotter, but the dehumidifier will actually make it hotter.