In addition to entertainment, a set of loose fitting clothing and cheap panties you don't mind seeing the possibility of throwing away from blood stains. My surgeon recommends a gown with front buttons or snaps (of course finding one that doesn't look like a bathroom robe or hospital gown is another matter).
I would recommend if possible a checked in bag which contains clothing, supplies, ect and a small carry on bag that has valuables which doesn't weigh more than 10 lbs total including the bag.