I can think of a lot of ways to be frugal, but most of them will actually involve food in some way. Yes, you can cut down on the energy you use and carpool to work, or sit in semi-darkness at home, but the easiest way to save money, for a family at least, is by cooking.
I know that it may seem odd, but even learning to make your own sandwich meats can make a large difference. My son heard the Mackenzie Brothers on the radio back in the fall and has been calling Canadian Bacon (a type of ham) "back bacon" ever since. About the same time, I purchased a large manual meat grinder intending to make sausages and bratwurst since they are so expensive to buy. I started gathering the necessary ingredients, one of which was a quick cure mixture found on the bottom shelf at the grocery near the salt. Morton makes a very nice one called "Quick Cure" that works like a charm. The package stated that the website has recipes. So I looked it up. Low and behold, Canadian Bacon was one of the recipes. Very easy to make, a pork loin, 5 days and a smoker. The smoker was no problem since my husband got me the smoker attachment for my grill as a Christmas gift. I cured my pork loin in a ziplock bag in the refrigerator for the 3 to 5 days the recipe called for, then I rinsed all of the remaining salt from the meat and took it to the smoker. I smoked it for about 4 hours, until a meat thermometer said it was done (180 degrees) and brought it in. I cut it in thin slices like for a sandwich and it was just incredible. About that time the kids came in from school and we wound up eating about 3/4 of a pound of the meat immediately. I bagged up the rest of it and froze all but one bag, to use for sandwiches. So, ham for sandwiches for less than $2.00 a pound.
The Morton site also has recipes for other cured meats like salami and pepperoni. Those are made from hamburger and can be cooked in the oven. Very easy to make. And they are about half the cost of store bought meats. My next project will be to try to make bacon.
I realize that most folks just don't have the time or inclination to do this sort of thing. But think about it for a minute. If you make your own sandwich meats, you know how fresh it is, you know what is in it, and you can feel good about serving it to your family. Can you say those things about the food you get from the deli? Or how about those little pressed plastic packages from the grocery store? Just how long has that stuff been sitting on the shelf? And the cost! I can find ground beef for around $1.89 a pound. Sliced hard salami is around $3.59 for a 12 oz package. I can seriously justify the savings when we eat as many sandwiches as we do. And it freezes well. I can make up 3 or 4 pounds at a time and split it into 1 pound bags and just take them out of the freezer one at a time.
Making your own food is very satisfying and oddly liberating. I don't have to run to the grocery store every time I need to pack the kid's lunches. I know what they are eating and when I find the meat on sale, I stock up. Freezers are wonderful things.
It may take a little bit of time, but int he long run, it is definitely worth the effort.