I've always been careful when it comes to buying groceries. I check the sale papers, the clearance sections and know that things like rice, potatoes and pasta can stretch one meal into 4. I've also canned my own food for many years. However I rarely use coupons because they are usually for items that are more expensive and for processed foods.
In the last year I made a major change in the way I buy groceries and it has saved me a lot. I started out by buying a bit extra if something was on sale, whether it was peanut butter, fruits & vegetables or meat, etc.. I would can or dehydrate the extra if it was called for. Many items can be frozen too if you have the room in your freezer. For example if you are buying one bag of rice because it's on sale, get a couple extra and store it in containers, food saver bags or those mylar bags you can find pretty cheap on Ebay.
I have bought chicken breast when it went on sale for 99¢ a pound, boiled it and canned it and the broth. Ready to eat meat in a jar for making sandwiches, casseroles, tacos, soups and more. Recently I bought beef roast when Kroger had it on sale for $1.99 a pound. I slow roasted it and canned it just like the chicken. Last week I canned leftover turkey and broth. When those large bags of frozen vegetables are on sale I pick up some extra and dehydrate them. When I buy celery I chop up and dehydrate the stalks from the old bunch and store them in a jar.
No matter what you are buying on sale, if you pick up one, why not pick up two or three. You will soon have a little stockpile in your pantry and you can now go shopping right at home. What happens after a while is that you are now pretty much only buying sale items, so the $100 a week you used to spend on 50 different things is now more like $50 on multiples of a few items that are on sale or clearance. Because you have a nicely stocked pantry you can still put a balanced meal together.
You can do this with any item, canned veggies, flour & sugar, coffee, etc. Even one extra will help you to save money in the future because prices will go up and you are buying at a discount today. Don't be afraid to check out the dollar stores in your area. I buy a lot of canned goods and fruit juices as well as cat food at Dollar General. Many of the chain dollar stores take coupons too. A 13 pound bag of cat food at $8.50 is already less than Walmart, take off the 75¢ coupon I had and I now have a great deal.
Though I rarely use coupons, I have gotten some on Ebay, like for the cat food. I paid $1.75 for 20 coupons. There are many sites online where you can print out coupons for items you like tough many store will limit how many you can use and some will not take them at all.
One last thing, you can save the most money by cooking at home rather than eating out. I love eating out, but if I choose to eat good food and not fast food I have to limit how often I eat out, that means cooking at home most of the time and taking my lunch to work. And I don't have to deal with lunch time traffic!