Found A Treasury Token (?)

Kieth12 calls it bingo

A fun find in the wild and worth saving in a 2x2 as you have done. Nice work!

Nice find Allseasons

I thought you were actually referring to this one instead reading the title. Visitors at the Treasury Building could purchase examples of medals; they could also be purchased at US Mint gift shops and via mail order sometimes. http://goccf.com/t/331969

You have a "Mint Set Token". This token is struck on a cent blank so the weight will be equvalent to the blank its on and is included in United States Mint Sets each year from sometime in the 1980's to the present. There are two types, one with a "P" which accompanies the Philadelphia Mint coin package of the current year and one with a "D" that accompanies the Denver Mint coin package of the current year. Both of these packages make one Mint set. They are found inside the mint sets which would have the date on the packaging and coins. The tokens themselves have no particular value usually although as with anything some collectors might buy them in uncirculated condition.

Denver version:

If its 2.5g as you stated then yes its a copper-plated zinc cent blank its on. All cents after 1983 would weight that amount, while 1981 and earlier are copper weighing 3.11g. 1982 had both. So its not copper like the pre 82s. The mint did not issue regular 10 count mint sets, 5 for each mint branch for the years 1982 and 1983, but did sell Souvenir Mint Sets (5 coin one branch) at each branch mint, Philadelphia and Denver. However the token is different: