Have the girls stamp a huge pile of cards and deliver them to your local nursing home.
OR- take your craft materials to the nursing home, and have each girl pair up with a resident for a craft project- something simple, like stamping on a picture frame or a decoration to hang on a door.
(Ok, confession: I'm biased, as I'm the Activity Director in a nursing home. But I can tell you that the residents LOVE it when the girl scouts come!)