Toddler Tamers

From Parenting magazine:

Practical discipline tactics for the Terrible Twos
Pacify public tantrums
Anyone who's taken a toddler anywhere knows that mortification waits around every corner. Meltdowns generally start around 18 months. Things to keep in mind:
Try to preempt common tantrum triggers (fatigue, hunger, boredom, frustration) by doing errands in the morning or after naptime, and bringing snacks and an unfamiliar toy.
If prevention fails, ignore the tantrum. Pretend the screaming doesn't upset, impress, or affect you, and he'll realize there's little point in continuing.
If all else fails, get out of there! Leave the grocery cart, grab your child, and head for your car. His meltdown may simply be a plea for a hug or some undivided attention, so give him both when he's calmed down.