Get 12 ping pong balls or practice golf balls. Write A on three of them, C on three, G on three, and U on the last three. Be careful... because the balls don't have an "up" side, C and U can look similar - you might want to put a line underneath each letter. Place the ping pong balls into a bag or a hat.
Now play Bingo - pull 3 balls out of the bag, one at a time. Have students translate those three letters into an amino acid and mark it on their Bing card if needed.
Return the balls to the bag, give it a shake and repeat.
You could write out all the 3 base combinations and pull them out of a bag, but I think the balls are more fun! It would be even more fun if I could get my hands on one of those lottery/Bingo ball machines...