In need of a sturdy handbag for books etc, I took one of my old Frakta bags and changed it in this handy thing. It took me about 15 min.
I folded the bottom to the inside. Cut of the sides, turned inside out and sewed it back together again. Make sure the bottom is folded like a pocket. At last sew the corners to form a box-like shape. Turn outside in: Ready!