O-Rings
Airline pilots or travelers often hang their BrightLine Bag off the front of their main suitcase by use of a J-hook (or sometimes a nylon strap that loops with a buckle) that is part of the main suitcase.
Slide the two pairs of o-rings onto the main handle of the BrightLine Bag and nestle the J-hook from your main suitcase so that the two pairs of o-rings lie BETWEEN the prongs of the J-hook.
This will keep the J-hook from sliding side-to-side on the main handle of the BrightLine Bag as you pull your main suitcase around, and will keep your BrightLine Bag centered on your J-hook.