Heat waves are basically the only serious thing here. There isn’t really much to surviving them for the average person. Stay where it’s cool, stay hydrated, don’t over exert yourself in the heat. All really easy things to do if you have a reasonable amount of security in your life. Most don’t bother except maybe making sure to contact elderly or otherwise vulnerable relatives.

Preparation is needed if you’re not financially secure. Maybe you’re homeless, maybe you’re too broke too cool your home, maybe a lot of things. I’ve been there before. To this day I’m still aware of places I can find shelter across the city and how to get to them, with and without public transport, in a hurry.

Mostly the answer is libraries but it depends where you are in the sprawl and how bad the heat wave is. Libraries are the usual answer, and they’re great during business hours but if the heat wave is really bad they’ll close before things cool down. I learned to get really good at loitering in shops and other private places while expending as little as possible without them moving me on.

Also where to get potable drinking water for free, you’ll be surprised how hard it can be to find in a pinch.