I got this idea from Mrs. Kings Music Room blog. Kindergarten students place a bingo chip or a button over a letter of the alphabet in a printout of the ABC song. When they sing the song, they make the letter covered with the button a rest. Then they continue adding buttons and singing again with more rests.
It would be fun to add more songs to as well (ie. Mary Had A Little Lamb, Baa Baa Black Sheep, Twinkle Twinkle, etc.).