More tips on what to do:
Give him a heads-up. Meltdowns occur when plans change. If a child knows what's happening next, he'll be more likely to go with the flow.
Help him roll with the punches. To bust him out of his mood, engage him in a favorite activity. For some kids, a back rub might do the trick.
Deal with the issue afterward. It's hard to be rational when we're mad, so don't try to get your kid to apologize in the heat of the moment.
Help him see the big picture. When he's calm, brainstorm about what he can do differently next time. He's got more perspective now than when he was a toddler.