One of our favorites is a real money saver. Mix ketchup with worcestershire (sp?) sauce. I do not measure, so it is just to taste, it makes a great steak sauce so comparable to A-1 that most people do not taste the difference!

I have found that having a box of commercial egg substitute on the shelf is also a good way to keep from needing to run from the store. Not as cheap as some other methods, but still slightly cheaper than fresh eggs (where I live, anyway).

I’ve also substituted a cupful of tofu when making pancakes or waffles–basically the same as using cottage cheese.

I’ve found that gluten-free websites, allergy-cooking websites, and vegan websites often have very creative ideas for substitutes. When we make our Sloppy Joe recipe that originally called for a can of tomato soup, we now use a can of tomato paste topped up with enough milk to make a cupful–and adjust the seasonings a bit. (It’s a good substitute if you have the tomato paste and not the soup.) I tried making tomato-paste-plus-milk tomato soup from the Tightwad Gazette and didn’t like it much; but mixed in recipes it seems to work.

I often substitute one form of tomatoes or other tomato products for another, depending on what I have or what needs to be used up. Our chili might be made with all canned tomatoes, all fresh, or a combination.

You also learn substitutions when you have picky eaters or there are other things you know you just can’t serve. I have a cucumber-hater who will eat zucchini, so we have zucchini in the salad instead.