We're impressed by the ambitious design of the Arkiv Field Pack, a modular bag system allowing "for easy customization of space and organization with the secure and simple attachment of independently weatherproof accessories utilizing unbreakable steel hardware."
Designed by San-Francisco-based Mission Workshop, the Arkiv system consists of a main rucksack-style bag offered in two sizes—a 20-liter-capacity Small and a 40-liter-capacity Large—and a series of satellite bags to choose from: A laptop case, a tool pouch, a cell phone holder, a folio for documents and writing materials, and a couple of add-on pockets meant to hold water bottles or random objects. There's even an optional additional shoulder strap, so you can turn any of the satellite bags into an independent one.
We wish that the following video offered a little less style and a little more explanation...
...but it appears that the smaller bags slide onto a webbing-based rail system on the main bags. Looks pretty nifty.
Mission Workshop manufactures these bags in the USA, and they come with a lifetime warranty.