ARM-mounted fill in the blank

On the Wednesday show you mentioned cramming the pi laptop into Leela's armband or a PipBoy2000. Way ahead of you. I've been thinking about what the new Apple watch can do with health readings. With the sensors, batteries, and computing you can (buy for/harvest from) cell phones and other portables, answer me this.

Forget "thinner and lighter than ever before." Just how much capability can you today stuff into Captain Jack's rift manipulator? Slots and pockets all around, adjustable straps, protective flap... As a computing device, this could be totally pimped out.
- Nathan