Holy shit...if that was my kid the minute he started screaming I'd have leaned over and whispered harshly "Be quiet or we're going home right now" and if he didn't then the cart woudl have tsayed there and he woudl have been taken home...even if he was kicking and screaming...that is crazy...
if that was my kid we would have gone immediately home where i would administer a spanking and dinner would have been a bowl of cereal. i have never experienced anything like that little tantrum.
My oldest pulled that 2 times. I just leaned against the wall next to him, let him finish - then we carried on. He figured out it didn't do diddly squat so he quit doing it.
Remind me to thank my son for never getting even close to that.
The few times he would act out in a mall etc I either took him to the nearest rest-room or another place with no on-lookers and had a talk (yup, talk) with him. That usually solved the problem.