They make shoes other than hikers? I bet next your going to tell me some craziness like theres watches other than suuntos and hats other than tan ones with american flags on them.
But seriously I always bring a GPS running watch. It combats the old team philosphy of "we ran for 30 minutes so thats a minimum 4 miles." A fat grip to put on a workout bar is nice ( similiar to this
Fat Grip)
Phone cards, you never know. Extra weapons cleaning stuff the bravos don't have (synthetic lube, bronze non marring picks, extra patches). I definately second the concealable holster, its hilarious when you see senior e-7's using their belt loops as a holster.
Your own sights is always nice such as a magnifer for your EOTECH or personal preference. Same goes with small things like slings and buttstocks.
Coming up in the rear is microfiber towels and a stove system(jetboil).