The cards can be pushed together to clean up.
Or you can play Dictation Cleanup. You and/or the students take turns singing and signing one measure for everyone else to find, putting each card in turn in a stack.
Daily Do Song Puzzle Cards Set 2 Dictation Clean-Up from Music Mind Games on Vimeo.
Or if you run out of time, do both: Sing few cards for Dictation Cleanup and then push the others together.