In this day and age, if you have an air conditioner in your home, the environmental answer to a heat wave is NOT to crank it down as low as it will go and refrigerate the house. The trick is to find the warmest temperature you can tolerate and keep it there, so you're not exposing yourself to a huge temperature shift from inside to outside.

Many homes in cooler climates don't have air conditioners. That is how I grew up, with a well-insulated house meant for cooler weather, not hot. Stay downstairs, move sleeping arrangements to the ground floor, and use box or oscillating fans to keep the air moving. Cover the windows in such a way to put up shade outside each window or patio door to keep the sun from beating into the house. The solar gain is wicked if you don't cover big areas of glass. Cross ventilation is good, if you can get it from a shady porch into the house.

A meteorologist here in Texas used to promote putting a sprinkler on the roof and running it at midday so the evaporative effect of the water would keep the attic and inside cooler. It does work but does involve figuring out how to get the sprinkler to stay put when the weight of the hose is bound to pull it back off the roof again. Do that trick advisedly, and only if you have ample water and water pressure.

If you can find such a thing as a mesh tarp, that lets about 40 to 50% of the light through, and put it up over your patio or exposed windows, this will let in enough light but mostly keep out a lot of the heat.

If you have an air conditioner you'll be using a lot of power, something that can be in short supply during hot periods. While you're suffering through the heat, remember that you need to tolerate as much of it as possible. In US measurements, I tend to keep the house at about 80 degrees when it's 100 or more outside. Before I go to bed I lower the thermostat to 78 to cool it a little more, then set it up to 82 when I retire. This way it's cool enough to get to sleep and I don't usually awaken as the house gets slowly warmer and at night the house doesn't warm up as fast. If you have air conditioning set too cool, the blowing from vents may wake you. A friend of mine uses the approach to cool the house as much as possible before going to bed, then turning off the AC, hoping the cool air will be enough overnight.

Small fans and spray bottles to dampen your skin or clothing to allow evaporative cooling is very effective. Fill several pots and containers with water in case pipes burst during the heat, so you can stay hydrated.

If you're in an area affected by more than just heat, such as a wildfire area, assemble things that can go quickly if you evacuate. I have a plastic hanging file box that has the most current household paperwork and bills along with banking information and such that can be put in the car along with clothes, water, electronics that can be easily transported (phone and charger, laptop and charger, and think about taking along the desktop CPU and leaving the rest on the desk. If the house burns down, what is in the computer can be used once you attach it to new monitors, printers, scanners, etc. Have clothing, medicines, pet food and pet gear ready to go, all in the car, if you evacuate.

If you're suffering, so is the wildlife. Clean any bird baths and keep them filled daily. If you do this every day you won't have a mosquito problem; they need 5 days for larva to become mosquitoes. Put plant saucers (for under pots) on the ground and keep them filled for birds, lizards, honeybees, and more. You'll find an interesting array of creatures willing to share your water if you situate yourself so you can see these water sources.