Geraniums are always a safe bet, they can withstand plenty of heat and don’t require much care (except dead heading) will also survive if not watered for a few days. I also have here (23) Antirrhinums ( Snap Dragons) that have survived being left out over several winters and still flower even better the following year in both pots and in the ground.
Pansies seem to droop really quickly when dry, I have some winter pansies now that I’m having to check daily. Picture of Snap Dragons, taken just now.
Same weather here this morning, poor plants don’t stand a chance.
I like sweet williams, especially the fragrant ones. I have them on a window sill that gets no rain, so frequently dry (pic below). I also find portulaca very good for difficult places with no care if you want a low growing plant that flowers for a long time - not the weed purslane, but cultivated varieties - pourpier in french. For higher plants I have a box that is a mix of gaura and verbena bonariensis, which the insects love and needs little care.