Sometimes kids at high school want to eat out with friends. Socializing is part of learning to adjust to the adult world too. Sure, they can bring a vacuum flask with rice sometimes, but they need to eat out sometimes too.
When I was a kid, my mom gave me so little that I still felt hungry sometimes (just enough for a bowl of noodles with fish balls, nothing left for snack or drink) and I could only go to eat with friends once a month. Then I went home and ate a lot for dinner.