I discovered that the store REI sells all different sizes of shock cord. Very nice for making lots of stuff.
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
If the o-ring breaks, just replace it with a loop of tied 2mm bungee just like you suggested. In the meantime, use the o-ring with no concerns...