What's the best way to control an unmanagable child in a public situation?

If the situation is really out of control just pick your child up and leave. Put them in their carseat and calmly tell them if they continue to act like this they do not get the privillage of going anywhere. My kids know I do not have to take them anywhere and If they are really bad I will tell them we will be staring at the walls and having no fun.:) Hope this helps.