We are a fan of contact paper over here. I will tape some of it down to our table or wall, pull out random bits of paper and tissue paper and let the girls stick (and unstick) whatever they want. Sometimes I will draw shapes on a piece of paper and put that underneath so Laurel will be challenged to copy the shapes with the bits of paper, though distraction will usually set in and she will create whatever she wants, and that is just fine.
This can be a one time project or you can stick a blank piece of paper on the back to seal it up and make a finished artwork.