Right, for this one I have used a length of fabric (mine's a tea towel), thread, something to use as a drawstring (shoelaces!!) and some pretty beads for the drawstring ends (nicked from little Chookie's toybox.)
Along the two short sides iron a 5mm hem and fold again at about 1cm and iron. This is the actual cord channel but isn't getting sewn yet!
....only up as far as the cord channel.
Measure 2 inches from one point and draw a line straight across. Stitch over this line and do the same on the other point.
Turn your bag the right way round and it should look like this.
For straps, you'll need two strips of fabric. Mine are 2in by 17in. Fold them in half right sides together and stitch up the long side.
Turn them the right way round press flat. Tuck the raw edges inside and press again.
Pin to the bag (the bottoms of mine are 3.5in from the top and 3in from the outer seam) and stitch in place.......
...like this. You can sew an additional cross inside the square if you think you need additional strength.
Thread your laces (or cord) through the channel at the top of the bag. Use one lace to go right round both sides (so it comes out next to where it went in) and start the second lace at the OTHER side seam so when you pull all four ends the bag gathers closed.
Add beads if you're girly and you're done! ::grins::