No people like YOU or Sheep. Fund his prison account. Then he buys these items. You do not eat them together. Yet there are prison inmates that become chefs. They take items like ramen noodles and make a special dinner. Or take 10 honey buns and put on icing and make a cake. Or make a dip with spam.
Point is the prison shop is considered like gold to prisoners that have nothing else. Since brown lunch meats that is served is not very good food.
That is why the shop does very well. So either people like you have to fund it or he has to make a trade for a skill (wink) such as making flowers out of toilet paper. Writing poems for inmates.