FWIW, I tried a $30/wk food challenge in Nomvember. I learned a lot. It's doable, but one can't waste anything and every food has to serve a nutritional purpose. I've upped it to $35/wk and it's not even hard to do.
We have a sailboat that I go stay on for a couple of weeks at a time. I always stop at the 99c Only store to buy my groceries. I stopped this last Saturday and spent $28 for groceries that will last til I go home this Saturday. I am eating well too.