I received an invitation to a wedding, and included in the invitation envelope was a bright, shiny penny. The couple asked that, when returning your response, that you include the penny after you've made a wish over it.
Their favors included a scratch-off lottery ticket with one of the lucky pennies taped to the back. There was a note that said something like, 'We appreciate your best wishes for us, and offer our best wishes to you, too. Good luck!' It was cute.
My ticket, unfortunately, was not a winner. Whoever wished on that penny didn't wish hard enough.
Still, I really liked the favor.