At a fabric store you will need to buy heavy nylon thread, a needle and some draw-string fasteners. If you can't find thread that matches your garment, choose a color to contrast it instead. The materials can cost anywhere from five to ten USD.
Sew the pouch inside out. Make the stitches tight and close together. Try and keep the spaces between each stitch the same. Sewing should take no longer than twenty minutes; you will need to tie a square knot at either end of the stitching.
I intended to use these pouches for cables and occasionally personal items. If you intend to use the pouch for electronic devices you will need to sew in an extra liner. Another improvement would be to add elastic to replace the string. The last photo in this set shows a pouch with the upgraded parts.