It was slightly different for me, had to first be registered on the poors / eternal renters list with the school, after which they'd give you a booklet of paper tabs (like pull-tabs or the old food stamps system), and you presented one of those to the cafeteria cashier after getting your tray of prison-tier carbs, saturated fats, and refined sugars.

Never had anything thrown out in front of my face, but got to sit and watch everyone else eat because I knew I wasn't getting shit without that little paper tab quite a few times.