Idea #19 Guess the weight contest. Place a coin on a digital scale and take a reading, cover the numbers and ask members to guess, indicating how many decimal points are required for accuracy and in what measurement system: grams, troy oz., etc.
Idea #20 Guess the coin by it's weight as displayed on a digital scale. Blur or cover the image of the coin and show only the coins weight from the scale. First to guess, wins. You can increase difficulty if you want to have the type of coin named, eg. barber dime vs. mer. vs. roosevelt
Entry #7: Guess the Denomination (Such as taking a coin from the Barber series and the people who correctly answer the denomination get put into a hat and a winner is drawn.