A kid knows when he's creating a scene. The first words a kid learns are "I want". He's hoping his mom is going to cave, because of the tantrum, and the stares she's getting.. The best way to dissuade scenes is not to get irritated, but to ignore them. My kid brother was an expert on screaming in stores. He'd put on a great show. BTW, he never did this at home. My mom would leave him screaming, and thrashing about on the floor. After a while, it occurred to him that making a scene was counter productive, he stopped.
Your post brings back such memories.
At home, I was much more tolerant of my children acting up and throwing a tantie, but dare they do it while out, that was a whole other story.
I laugh thinking about it now, how I used to round-up the gang, and with them all in a group, I'd tell them, "mommy has to make a trip to town today, who's all going to be good when we're out"?
I'd remind them, "I don't want to hear any whining and complaining, if you're coming with me today, you're going to be good and behave, or we're coming straight back home".
I used to do simple little things for them to remind them how good trips out of the house could be with mom, and for the most part my kids understood and were receptive.
On sweltering hot days or when sub-zero temps hit, calling up a babysitter was automatic for me. No kid needs to be subjected to trying to keep up with an adult when they're zapped of all energy due to the heat, thirsty, or trying to waddle around in bulky winter-wear.