I have a long-haul flight with Scoot airline, and they have this weird rule:
Consumption of outside food and beverages is not allowed on board.
I've even read reports that Scoot flight attendants can actually ask passengers to put their food away.
I don't know what you think about this, but I'm going to bring some non-offensive sandwiches anyway. Now, what would be the worst-case scenario if a flight attendant asks me to hide my sandwich, but I disobey? I can't imagine any sensible way to prevent me from eating, given that I don't cause any distress to other passengers.