HIKEMAN Backpack Shoulder Strap Pouch - Smartphone Strap Pack,Waterproof Backpack Strap Pocket Attachment Bag for Hikers,Small Crossbody Bag Waist Pack for Sports Hiking Camping(Black)

That Hikeman one looks neat. Purple 😍 Looks like they copied the attachment design from the Montbell shoulder pouch but theirs also has a gatekeeper ring on top which will hold it in place so long as the strap has some attachment points, which most do... though the "very lightweight backpack" I was thinking of doesn't :( Very neat that the front of that one can hold a phone or even water bottle.