Step 7: Done!
If you're wondering about how to effectively turn the reactor on and off if the battery pack is under your shirt, on your back, I'd say don't worry about it. The string of lights I use runs on 4 AA batteries and I went to a party with the reactor turned on for the entire time and it never died (at least four hours).
Anyway, with this reactor, you can be casual Tony Stark and just throw on some nice slacks and a watch to go with your shirt.
Or you can be Prisoner of War Tony Stark and dirty yourself up a little bit, get a green army jacket, wear a drab-colored beanie (grey, olive, brown) grow out a little beard, and wear some beat up pants/shoes.
Depending on how thick your finalized reactor is, it might behoove you to NOT hold your shoulders back as much as you probably do normally (otherwise your reactor will stick out against your shirt and look a tad strange). Bad posture can make the reactor look more like it's a part of your chest rather than sitting on top of it so -- for once in your life -- it's perfectly fine to slouch.