We don't have an air conditioner at home so with the 40+ temps that Melbourne experienced last week, I wet a towel and wiped down our cat every couple of hours to keep him cool. He also doesn't drink a lot of water, so using a syringe I squirt a little water at a time into his mouth so that he didn't dehydrate. We were very relieved when it cooled down again!
I actually leave the air conditioner on for them if it gets above about 32 degrees. I have an old dog and because he is used to being inside with the air conditioner on, I feel sorry for him if I go out and don't turn it on!
My younger dog is far more resilient and I would not leave it on if I only had him.
Several bowls of water, in case a bowl is tipped over.
Pets generally have their own cooling systems, however if I know there is going to be an awful hot day then I put the air con on in the morning before leaving, and I leave work as soon as I can to get home to check on my pets.
All my pets are indoor pets. I don't believe in keeping pets outside.