Martha Stewart Living, June 2013
Cut two 9 1/2-inch squares of fabric and two 2 1/2-by-12-inch strips.
Sew squares together (right sides facing) along three sides. Press side seams open. Fold over top edges 1/4 inch, then again by 1/4 inch, and press. Sew all the way around. Turn bag right side out.
Fold strip in half widthwise (right sides facing), and sew along one long side, with a 1/4-inch seam allowance, creating a tube. Turn tube right side out and press. Fold ends of tube under by 1/2 inch, and press. Repeat with other strip.
Pin ends of strip to bag, about 3 inches in from the side and 1 inch down from the top. Sew in place by stitching a square that’s 1 inch wide by 1 inch high, then sewing an X within the square. Repeat with other strap.