if you are out and about and carrying a black-body camera, and it's hot, cover it with a hand towel.
I learned this one the hard way. In my film days, in 40C+ degree tropics. Cooked emulsion isn't fun to try to process.
Also last week in Malaysia,when I was out in the sun in a high-30C day. Luckily for me, SD cards don't need them processing in a Jobo.
Oh. And wear a sun hat (not a MAGA cap, please!). Not really photo-centric, but as one other poster has written, a sun cap/hat can be a nifty lens shade.