As promised here are the instructions for a drawstring bag.
1 - Decide on the size of your bag and measure and cut the fabric accordingly.
Tip: when you want to cut a strip of fabric, measure it and make a small cut and then with your hands on both sides of this cut just rip the fabric. You'll see that although the fabric frays a little you'll actually get a perfectly straight cut.
2- Make a little hem both at the top and bottom of your strip.
3- Choose the ribbon you're going to use to make the tube or path for the thinner ribbon and sew at at the top and bottom as close to the edge as possible.
4- With right sides of the fabric facing each other, align the ribbon you've just sewn and sew the sides of your bag.
5- Trim all the bits so it looks nice and tidy. Turn your bag inside out.
6- With some very sharp scissors make some cuts on both sides of the ribbon tube. This is where the thinner ribbon is going to go. Do the same on the other side.
7- With the help of a safety pin, insert the thinner ribbon going all the way round. Do the same on the other side and hold together with a knot.
And there you have your drawstring bag ready to be used 
