Woah, woah, woah miss Lippy.... I'll work if it's worth my time... However, I assume many many many people are getting Kennedy halves and doing this so chances are slim.
There is a look and feel of silver and gold coins that goes back thousands of years. You could take a roll of 1921 Morgan silver dollars and go back in time to the Roman Era and use them to buy things. The Romans would be able to reconize that these Morgan's were high grade silver and much nicer than their primitive coins.