SD1K nailed the list of essentials, though I personally would go for a window seat so I have control of the shades and a wall to lean against.

All I would add is, get up as early as possible the day of your flight, I'm talking like 3AM if you can do it. That way you'll be as tired as possible when you get on the flight. EWR-LON is only going to be in the neighborhood of 5-6 hours in cruise flight (the part where you can hope for undisturbed sleep), so eat before the flight, pop the Ambien as soon as they reach cruise altitude (don't take it before departure, you want to be fully conscious if there's any type of emergency on the ground or right after takeoff), and zzz out for 4-5 hours.