What's a Mom to do when her kid has a public meltdown?

TMZ caught Gwen and her son on the streets of New York, happy as could be until it was time to go. Then she had to stuff him into an SUV as he started to wail. Who can't relate to that? Is there anything that can be done to tame a toddler tantrum, especially one that goes down in public? We turned to psychotherapist and Mom•Logic friend Jill Spivack for advice.