On the way to HKG, you are required to remain onboard. The aircraft is refueled, cleaned and catered and there is a crew change as well right before passengers joining from YVR board.
As for meals, 3 meal services. One after departure from JFK and 2 from YVR. All a la carte since you'll be in F. So feel free to eat at anytime as you wish. Caviar is only served on the longer sector.