Rachel Jonat has a book out on minimalism, but it also has many good tips on frugal living. The two frequently go hand in hand. Do Less. You can find it on Amazon.com. (Sorry, I couldn't figure out how to link you directly to the book.)
One of the tips that has proven to be most helpful to me has been Jonat's idea of specializing in just half a dozen dinners. Preferably ones that are cheap and that you really enjoy and that are nutritious. This version is more of the plant based kind.
In the morning have oatmeal for breakfast. You can make your own just as easily as buying those little packets with the added ingredients. If you must have cream and sugar, add half and half or milk and sugar from the bakery section. It will save you a great deal of money in the long run. If you pop it in the microwave it really will take no longer to cook either!
For lunch, take a sandwich or leftovers to work. Since I usually have twice the food I need at dinner from living alone, I eat leftovers for lunch each day.
For dinner on Monday: Italian curry. This is made with brown rice and lentils. Add fresh onion, garlic and curry powder with other seasonings halfway through the boiling process. When the lentils are soft enough to eat (not before!) add a can of diced tomatoes or puree.
Tuesday: Poor Man's Meal. Fry onion and two potatoes. Then add eggs, your favorite cheese, and a little salsa. This can be good with bacon or other breakfast meats as well.
Wednesday: Vegan chili. Simply made. Add a can of corn, a can of black beans, and a can of tomato sauce. Cook well and season to taste.
Thursday: Whole wheat spaghetti with homemade sauce. Saute a diced onion in olive oil or canola oil, then add tomato sauce and seasoning. Serve over spaghetti, topped with cheese.
Friday: Tuna rice casserole. Cook brown rice, mix in can of condensed cream soup with one can of water, add spinach or broccoli and can of drained tuna. Top with cheese.
Saturday: Soup made of precooked mashed potatoes, spinach, and chicken stock.
Sunday: French toast, leftovers, or repeat favorite dish.
By sticking to this menu, you can avoid lunching out due to necessity. You also know whether you need a certain item and can cut costs on unnecessary things when you shop. It also helps when you buy in bulk to save money.