At some point every parent is going to have to face the public tantrum that every child is bound to have.  There are many different options to take when this happens.  I have seen many of then applied.

The one to avoid is giving in to whatever the tantrum is being thrown over.  If your child wants a candy bar, or a car and you have already said no then stick to it.  The one time that you cave in to a tantrum will insure that you will have many more.

Sometimes this is easier said that done.  You don't want people to think you have a bad child just because they are screaming, or you just want them to stop so that you can continue your shopping.  The truth is that  people are secretly applauding the parents that don't give in.  Whether you have chosen to ignore the behavior of the tantrum, or just leave the store.

There is more to it than what other people think, there is the message that you send to your child.  Children need to understand that just because they "want" something "now" doesn't mean that they will get it on demand.  You are doing them a favor by not giving in to it.

Methods to use would be: leave the place of the tantrum, ignore the behavior (if possible), put them in a corner (if possible) and you can do all these things until the child calms down.  In some extreme cases  you may just need to take the child home and try the outing again later.