not true at all.
you can bring snacks such as granola bars, fruit and grain bars, potato chips, cheese crackers, cookies.....
you can bring a sandwich if you want.
and you can bring drinks like a bottle of water, a bottle of soda, a bottle of juice...
just make sure3 you are not bringing in any glass containers unless its a baby bottle or jar baby food.
they even allow you to bring in small soft sided coolers to keep things cool.
of course there are limits where you cannot do something extreme like bring in the ingredients for chicken Parmesan and expect you can whip it up in one of the restaurants. (obviously a very out there example but you get the idea)