Those without A/C, what are your tips to stay cool during the summer?

Funny to see this question here a few weeks ago did I see someone link this https://m.youtube.com/watch?v=Nqxjfp4Gi0k&feature=youtu.be

The video shows how to create a salt based pcm (phase change material). You can also buy packs like these but I thought it seemed more fun to create it myself, so it will be my summer project when the heat is not barrable. I think Putting it under a cap would do wonders.