There's merit to the government food assistance (SNAP in the US) idea, though if you're trying to ban "junk food" from SNAP you're going to run into definition issues. Banning things like Twinkies and cola from SNAP is one thing, but "junk food" may also include ready-made ultra-processed food depending on your definition, and that may be the only type of food typical SNAP recipients can use (e.g. homeless who do not have access to cooking, people who live in food deserts). There is also a valid concern about micromanaging the food people eat, because SNAP recipients are normal humans and we tend to give normal humans leeway to indulge in a treat every now and then.