When I get to live in my own apartment (I live with my family), I'd do groceries every 1st and 3rd week of a month during Sunday. I'm hoping to spend no more about $50-$75 a month, since I'd buy 4 boxes of Digiornos Pizza every first week of a month, 1 box of Lipton Tea for 1 1/2 month (first week of Janurary and 3rd week of February, for example), 1 hamburger meat per week, a pack of 10 hotdogs for 2 weeks, mashed potatos, eggs, milk, etc. for two weeks, etc.
It's all about money management, food management, and planning ahead about what food to get.