Seconding everything everyone else said (except I'd suggest some drowsy-making/anxiety-reducing meds in place alcohol -- I shudder to think of the possibility of an in-air hangover, and that's entirely possibly with 16 hours), but also try to stand up and walk around as much as possible.

And you probably know this, but once you get through the security gate, buy a big bottle of water to bring on the plane with you. Being stuck with dinky little plastic cups incapable of hydrating anyone beyond a toddler on the dry pressurized climes of a plane is not fun.