I think they come in cellophane Uncirculated (not proof) U.S. Mint sets Edit #1: see link here Edit #2: see another Cointalk thread here
I think these are included in Mint Sets. Someone broke open a mint set. I looked this coin up online and it's definitely not a token or any other kind of "coin".
Found this on the interweb: Token: US Mint Set (P or D) A Mint Set from the US Mint contains uncirculated specimens of current coins. The mint makes oodles of them and sells them to collectors at exorbitant prices. Packaged with some of these sets is a small copper token with P (Philadelphia) or D (Denver) on one site. Enterprising coin dealers break the sets apart and sell the uncirculated coins separately. What is left, then, are oodles of unsold P or D tokens. You can buy them on eBay in lots of 50 for a few US dollars.