This was a really quick project and I think we'll get good use out of it. I made a simple lunch bag for Bryn to use in nursery, picnics, and other outings. I saw the basic pattern for it during our last date to Barnes and Noble. (I think maybe in a Martha Stewart book?) The main panel of oil cloth is 29.5 x 8 inches. And the two side panels are 12.25 by 5 inches. You just sew the side panels to the main panel, with a 1/4 inch seam allowance. Cut slits at the corners, or else the corners won't work. And then add velcro so you can close it. If that's confusing, there's a simple pattern for a lunch bag on the Martha Stewart website.
P.S. One tip for sewing with oil cloth: Put tissue paper over the oil cloth as you sew, to prevent the oil cloth from sticking to your presser foot. It tears off really smoothly once the seam is done.