Pillow cases are really strong and can be useful for many things.
I have seen people make aprons, tote bags, drawstring bags, dog beds, etc.
I always handed my kids a nice pillow case for their trick or treat bag, you won't believe the weight those things can hold in candy! lol. I buy them at sams in a big 12 pack and have them on hand for the kids friends too. You know there is always that kid that comes over to go along trick or treating without a bag lol. Use as is, or decorate a white one with ghost face.
They are great as covers for heating pads, beach totes. They are handy laundry bags when the kids go to a sleep over or for vacation, to keep the dirty/clean organized.
You can also decorate them, and use them as gift bags. The recipient can reuse them, save the world! lol.
this is a great little tutorial for making this pretty pillowcase tote, which you could use as a grocery bag or anything! http://blog.creativekismet.com/2007/10/27/pillowcase-tote-tutorial/