Here's a little rambling of some of the tactics that have helped keep our food costs down.
-Learn how to cook! If you can cook, you can take several staple or bulk-bought items and turn them into a meal. If you cannot cook, you will have to rely on restaurant or store-bought prepared meals or meal "kits" that cost more and are much less healthy for you. If you can cook, you can also recycle leftovers into new meals instead of letting them linger in your fridge until they turn green.
-Find the space and keep a well-stocked pantry and freezer (see

http://www.savingadvice.com/forums/general-discussion-food-e...). Although it will cost more in the short-term to build up your stockpiles, having the items you need on hand will stop you from having to make quick trips to the store to buy one or two items (which probably will not be on sale when you need them, and which will probably encourage you to pick up a few more things while you are there).
-Be open to substitutions. If you don't have sugar, will brown sugar do? Can you use crushed tomatoes instead of diced? Will hamburger work instead of sausage? If you are flexible, it can avoid last minute grocery runs.
-Keep a price book. Although I no longer do this (I have the prices I need in my head now), it was incredibly valuable to me when I first started trying to save. Keeping track of prices on items you buy often will help you know when you have found a bargain. If you don't know how to make a price book, read The Tightwad Gazette by Amy Dacyzyn.
-Garden. The cheapest food there is. I just saw an ad today for seeds at Walgreens - 10/$1 with coupon. Ten different kinds of veggies for $1 with some work (or fun, depending on your attitude) involved.
-Find a cheap source of food. No, I don't mean the dumpster (although I have heard of some enterprising people getting food there). Do you have a local scratch and dent store? An Aldi's? A bulk seller? About a year ago, I found a Mennonite-run store about 4 miles from my house (how did I never find it before???) that sells not only bulk items, but exppired brand-name foods. I took my mom there recently and she was thrilled to find Ballpark hot dogs for $.59/package, which we immdiately threw into the freezer. Many items are good past the expiration date. Whenever I'm in a "typical" grocery store, even when I'm not there to buy meat, I do a quick check through the meat aisle for marked-down meat that is near the sell-by date. It is immediately used or thrown into the freezer.
-Be creative! Instead of throwing away that last bit of leftover veggies, throw them into a "soup bowl" in the freezer for your next pot. Take a half-eaten apple (if you have kids, you'll know what I mean) and cut off the eaten parts. Slice it up and serve it back to your kids later. Try your hand at pancakes or waffles from scratch instead of a mix. You'll be surprised at how much better they are, and how they are not as much work as you thought.

What's absent here? A section on coupons. I rarely use them. That doesn't mean they aren't helpful - but they just aren't particularly helpful to me since they are not taken at the stores I usually shop in. However, they can be a valuable money saver for some. I just found that they took to much of my time for minimal returns.