Cut three rectangles of fabric measuring 9.5 inches by 11 inches. Sew a 1/2-inch hem on one short side of each of the three pieces.
Stack all three pieces of fabric together neatly, with the hemmed edges together and the two outside pieces facing wrong-side out. Pin the pieces together along the unsewn edges.
Sew a 1/2-inch seam along the three pinned edges. Remove the pins and clip the corners.
Turn the sewn bag inside out from the pocket with the two right-side-facing pieces. The pocket where the wrong sides face each other inside the bag will be towards the front; the other is the hidden pocket that is held away from the audience and where business is performed.