How about some leather work gloves & a small pry bar for if you had to escape through a blocked/jammed door & or broken glass or other obstructions.
For the space that theyd take up, a garbage bag & some paracord would be woth chucking in the bag, too.
How about a rolled-up Platypus bottle that you could fill from your office cooler/bathroom/water fountain? (Some puritabs would be handy too)
The pack he is using would not hold many of the things you suggested. Google "Maxpedition M1" and you'll see that most of us think of something bigger when we think of waistpack.

Great idea btw...I was contemplating selling mine because I haven't used it like I thought I would...I may be rethinking that and setting mine up in a similar fashion. Thanks for the idea!
What are you using the water for? If it's for drinking, the Datrex is probably not worth the space...that amount of water won't get you far. If it's for flushing wounds...that's a different story. You might consider povidone iodine wipes (don't remember if that had been suggested). Can't wait to get home and see how much I can stuff in that thing!