The key is find items that are on extreme discount like BOGO or 50% off (same thing). This can really help you drop the cost of your daily items. You've got to eat what the grocery store gives you, just like nature. You can supplement this with basic cheap items like beans and rice and also those burritos shown above. The regular price of those is 0.59 with (no tax) and they provide 310 calories each of protein and fiber.
Just got some beans and rice today, so we'll see how that goes. I've also noticed how incredibly cheap some items are and have gotten pissed to find out just how much the restaurants are making off of me! When I can consume a giant plate of spaghetti for $1.13, but the restaurant charges me $10, plus tax, plus tip? Screw that!