It is incredibly simple and will hold a days worth of frantic shopping or a wiggly Dachshund or maybe an infant but I haven't tried the latter.
You start with two 30" x 40" rectangles of fabric. Serge them together, wrong sides together. An inner layer, like batting, is not recommended as it may make the bag too bulky. On the 40" sides create two button holes about 1" long on each side of the bag, about 10" from each end. Fold the button hole sides into the interior about 1 1/2" and sew down creating a casing. Thread a cord about 30" long into the side casings through the buttonholes and tie securely. At the top of the bag, create two other casings about 2" wide. Thread two more cords or straps through the casings to make handles. The cords/straps should be about 50" long. My directions may seem odd but here is the one I made the other day. The embroidery was a test for an embroidery pattern I like. The exterior is a rough brown cotton homespun. The interior is a commercailly available orange batik. I think it is best worn acroos the body rather than hanging from a shoulder.
PS. The pattern also included a pocket but I did not add one. The recomended size is 4" x 8".