When was Cooper's drinking glass removed?
Cooper ordered his drink from Flo while on the ground in Portland. He passed the note beginning the hijacking just as they were readying for takeoff.
I would have to assume that he didn't order the drink, drink it (and spill it), and have a flight attendant take his empty glass away all before the note was passed.
Which leads me to think he was still in possesion of the glass at the time he began the hijacking.
At what point was his empty glass retrieved from him? And who retrieved it?