I have to go against the grain here and say I think that F pax should be welcome to snack boxes for free (assuming this isn't stuffing a bunch of them into your carryon to eat/sell later
). It's a really silly degradation of a premium cabin to nickel and dime for food from the back of the plane.
That being said, most F pax shouldn't be wanting Y food items or there's something wrong with the catering up front.