Well, the pocket is very stretchy, so you could certainly shove a few things in there, but it's narrower than something like the GG Gorilla pocket. It's 6.5" wide at the top, and 9" at the bottom, 11" tall. I keep it lined up with the original seams of the Ion for a clean aesthetic. You won't fit major volume in there, just a few convenience items.
I didn't get around to adding the LL3's, but would be willing to add them before shipping(no extra charge). I also added some shock cord and cord-locks on the strap to attach a water bottle.