Jog my memory, please...
Wasn't it sometime in the '70s when the US went from pure copper pennies to some zinc alloy?
Those old pennies may actually be worth more. They make a purtier ringing sound when dropped on a hard surface, that's for sure. The "new" ones sound like slugs.
Currently, I have only one use for pennies. It's an old family (possibly ethnically based) tradition that it's bad luck to give an empty wallet or purse as a gift. So we put one shiny penny, a new one or an old one that's been polished, in the gift, as a wish for wealth for the recipient. I guess, if pennies go away, we could make do with nickels, but they have always been such an ugly coin...