My guess is that Economy will have a cold meal, like sandwiches. You can probably request it at anytime they aren't in meal service prep/cleanup, but they will probably also have a flight attendant mid sleep wander through, quietly handing out sandwiches to those that are still awake
. No idea if they will do that, but on longer flights I have had that happen before with other airlines.
If I was flying economy for this flight, I would definitely bring on some snacks!