These are so easy to make and have a ton of applications for use. They can be made in any size too.
Press the top of each raw edge under, then press the edge down again a little larger than the width of your ribbon...probably about 1/2" . Take some seam sealant and go over the drawstring openings.
Edge stitch along the casing edges on both the front and back of your bag. Then stitch the bag together around the outside edge with right sides together. Starting just below the drawstring opening and back stitching to secure, continue to the other side and back tack at that drawstring opening....otherwise you won't be able thread the ribbon through the casing.
Then I did a zig-zag stitch around those seam allowances just to strengthen them and keep them from raveling, also starting below the casing and stopping before the next casing on the other side.
Turn the bags right side out and use a bodkin to thread the ribbon through and then tie a knot in both ends to keep them from being pulled out.
Here are the bags with each puzzle.