Cotton yarn, such as Handicrafter or any stiffish type yarn. i.e. could be hemp, cording, stiff ribbon.
Hook, 5mm or so.
Chain stitch 18 chains,
Single crochet into each chain and work circular 9 rounds or until size needed to fit business card.
Last row, work single crochet to where you would need a button hole for the closure. Chain enough chains for button hole and then continue single crochet to side edge.
Cut and Secure last stitch. Hide the yarn tail within the crochet stitches of the body of the bag.