During World War II America rationed various types of food, and issued ration stamps granting citizens to purchase given amounts of specific types of food. OPA tokens were small 'coins' used to make change for ration stamps.
OPA stands for Office of Price Administration, and each token had the inscription "OPA * Point * Blue" or "OPA * Point * Red" around the inside of the rim, with a "1" in the center; both sides were the same. Blue tokens were used for processed foods (canned, bottled, or frozen); red tokens for meats and fats. They were worth one tenth of a ration stamp, and were small disks slightly smaller in diameter than a dime (16 mm in diameter, 1.40 mm thick). They were made from vulcanized fiber (i.e., a type of laminated celluloid), and were colored as the names would suggest.
OPA tokens are collectible, and broadly fall under the umbrella of numismatics. They were issued only from 1944 to 1945, and had a somewhat cryptic pair of capital letters on either side of the 1. Collectors usually try to find a full set of these letters, consisting of 30 different red tokens and 24 blue ones. A token is generally worth about 50 cents today, although some of the rarer letter combinations can sell for over a hundred dollars.