Sling Strap/Bag - Can't find

My boyfriend and I have a silly bet going over a sling strap/bag that he wants to use when riding.  He describes it as a sling strap, similar to an ammunition belt, that is only big enough to carry essentials...keys, phone, MP3 player, etc.  He says that it really isn't a "bag" and that the actual "strap" is less than a foot wide.  Does anyone have any idea what I'm talking about or where I can find it?