Wallet
Keys
Phone
Pocket knife (fer widdlin'!)
Pen
Penlight
Pocket protocol book
Shears (because I swear those bastards grow legs right before you need them)
Stethoscope (just in case I hear some really awesome music and it's far away)
I don't give a crap if this guy carries all that stuff, to each his own. Furthermore, I'd be extremely thrilled if he had something that I needed on a scene where we weren't near the rig. Good for you, buddy. Just remember to have your cuff key on you too, in case you're using them for "non-traditional" reasons.