What this little bag lacks in visual excitement, it makes up for in ease of sewing. It's a 10 minute job and it utilizes a material that everyone has sooner or later: worn out jeans.
Cut off the bottom 12" (30cm) of one leg of the jeans.
Turn inside out. Sew a seam to close up the cut edge.
Fold over the top of the bag. Find a pleasing proportion.
Mark the desired location of the button loop and the button.
Sew on button and button loop.