To start, choose a pillowcase that has a channel at the top, this will be the pocket for your drawstring. You will also want to choose a sturdy ribbon like this grosgrain that won't fray or tear.
Use a hot iron to press the pillowcase and ribbon so it's nice and flat.
Using a small sharp pair of scissors, cut a slit in the outside layer of each side of the pillowcase channel on both the front and the back. As well as the bottom two corners right on the side seams.
Attach a safety pin to one end of your grosgrain and thread it through the channel.
When there is enough ribbon through the channel to make both the drawstring and one handle, cut it off and carefully pin the end in the channel to hold it while you repeat the process on the other side.
On the flip side start your channel so your handle will end up on the opposite side from the first.
When both sides are finished, slip the ends of your ribbon into the slits on the bottom corners and pin them in place.
Now either hand or machine stitch your bottom corners in place as well as the one side of each of the upper channels.
That's all there is to a cute pillowcase backpack! I'm Mrs. Fixit and it's just that simple!