Becky from Patchwork Posse shares a tutorial showing how you can turn a couple of t-shirts into a cute backpack. She uses two shirts for each bag to yield enough fabric for a lining. All of the fabric you need to make this will come from the two t-shirts, including the fabric for the straps. The lining makes it extra sturdy and hides all seam allowance between the layers. Go to Patchwork Posse for the how-to.
[photo from Patchwork Posse]