Adding interest to a plain bag can be as simple as attaching an appliquéd design. It's a lot easier than you may think.
Lauren, from Molly and Mama, shows how to make a Fabric Flower Appliqué Tote, with instructions for sewing both the appliqué and the bag. The template for the floral design can be downloaded as a PDF.
Have you tried appliqué? It's a great way to use up very small scraps of fabric.