The packable backpack for when the weather means business. Roll top plus a zip, seams fully taped inside, and it stuffs down to nothing in your travel bag until you need it. This is the let's-go-to-Thailand one.
The packable backpack I'd reach for most of the time. Simple, light, weatherproof enough, with a nice pocket up front and a quick-access stash on the top back. It disappears into your travel bag, then becomes your daypack on the other side.
The accessory every traveler needs. It packs down to nothing in your travel bag, then becomes your daypack on the other side. Extra capacity when you need it, no bulk when you don't.