My family of 9 eats for $3 to $6 a day ( .40 to .80) per person per day.
We do this buy buying in bulk, growing a garden, and eating less expensive meals. We drink water at meals and throughout the day. I keep six 2 liter bottles in my refrigerator that I refill with water from the kitchen faucet, so that we always have plenty of cold water to drink (we never have to wait for the water to run to get cold, and the chlorine taste in the water dissipates as it sits and chills).
Some of our meals cost more than others. More expensive meals are averaged out by others that are less expensive (for example, it costs us .22 for 9 people for breakfast in the morning when we have oatmeal with brown sugar). Many of my meals make leftovers, which also cuts the cost over multiple days. This allows some days to be over $3, and other days to be under $1.
I base my meals on what I have on hand. If I don't have it, we aren't eating it. I only purchase items at the lowest prices, and when I have money to go shopping. Many weeks, and sometimes months, I don't do any shopping at all.
Check out my seasonal menus that show what we're eating each season of the year. If you're unable to do any shopping at all, you can get ideas from my Strictly Pantry menu.