These were a quick easy treasure bag I made for the girls at my son's birthday party. They would be easier to make bigger, but they were still pretty easy.
2 pieces of string I just eyeballed it, it is going to be doubled so make sure it is long enough folded in half to be the length you want probably about 12 inches or so for each string
Sewing machine or needle and thread.
6" x 10" piece of fabric and coordinating thread
Then take your cord and lace through the holes on each side. Go through the two holes on one side and out the holes on the other side. Put your fingers inside the bag and pull until tight but not scrunched up.
Fold over the top over to cover below the slits on the inside of the bag. I used one pin on both sides to hold in place. Then being careful not to stitch on the cord or stitch your bag closed, start sewing at the seam and go all the way around securing the fabric with the cords inside. Back stitch when you come to your starting point. Trim your edges and tie the ends of the cord off on each side of your bag.
That's all there is to it. A bigger bag than this would certainly be easier, I just wanted the ones I made to be the same size as the ones I purchased for the boys at Oriental Trading.