Stella from The Golden Adventures of a Very Dark Horse shares a tutorial over at Moda Bake Shop showing how to make a play mat that folds up into a backpack.  She uses simple piecing to create fields and ponds on the playmat.  When your child is done playing, it folds up into a backpack.  Get the how-to.

[photo from The Golden Adventures of a Very Dark Horse on Moda Bake Shop]