From Learn MYOG:
Exploring urban areas or gearing up for a bikepacking, a stem bag is a handy bit of kit for stowing nearly anything: snacks, water bottle, sunglasses, coffee cup, a phone, gloves, a favorite post-ride tall boy. This intermediate-level MYOG project is a great entry into a fully custom bikepacking setup. Also known as a feedbag, our completed bag measures roughly 4" (10cm) wide and 7" (18cm) tall.
Cylindrical lined feedbag with closure external pouch and webbing to mount on any bike for one-hand open and close.