Today I saw one of those cheesy Facebook ads for a personal fan a builder would use on his belt to blow air up the back of his shirt. Normally I would ignore, but on Saturday the heat in the venue was stifling, especially for the first set.
Most of this sort of ad are either a con or ridiculously expensive. I did a quick google and found similar products all over Ali Express, including one for under £9 delivered, cheap enough not to weep if it's crap or doesn't appear. It seems a sensible thing to keep in my gig box, just in case, plus it functions as a power bank which could save the day. There are more basic ones on Amazon for even less.