I'm totally on board with this. Some of the things I no longer buy at the store are:
* Stock, usually a mix of whatever I've got leftover and shoved in the freezer (chicken and ham bones, veggie trimmings). Boiled in my biggest pot all day. Spoon hot into mason jars, with the fat, which solidifies into a nice seal that can be scooped out before use. They last in the fridge for two weeks at least.
* Spaghetti sauce. Tomato paste and/or crushed or sauced tomatoes, water or stock if needed, some veggies, herbs, salt, and pepper.
* Salad dressing. Drizzle some vinegar/lemon juice/other acid and olive oil, with some salt and pepper. I have a bottle with various dressing recipes printed on it if I want to get fancy.
* Granola bars. They're so good homemade, and much less sweet than the alternative, even with agave and coconut. I use bulk ingredients as much as possible and no dried fruit, which keeps the costs down. I also cut banana bread into "sticks" and give them to the kids. Good use for bananas that have turned the corner (as are smoothies).
* Granola cereal. I just crumble up two of the granola bars with some milk and I'm good to go. :)
* Baked goods of most kinds (crusty loaf bread, hamburger and hot dog buns, cookies, cobblers). Easy recipes abound.
* Hot chocolate mix. Regular milk chocolate, heated in the microwave.
* Microwave popcorn. Big glass bowl, handful of corn, put a wet paper towel on top and a light plate if it's going to bug you that some of the kernels jump out. It takes longer to finish than regular microwave, but tastes great. I haven't tried it without the paper towel yet, but that's next.
* Pizza. Every Wednesday night like clockwork.
* Soup. There's just no comparison. It's like a completely different food.
* Canned beans. Soak overnight, crockpot some the next morning for dinner, freeze the rest for later.
* Instant oatmeal. Just make a big pot of rolled or steel-cut oats and scoop some out every morning.
* Frozen french fries. Microwave whole potatoes until they've started getting soft. Slice into wedges. Rub with olive oil and salt. Bake at a high temp (say, 425F) until they're crispy on the outside.
I'm sure there are others, but this list has gotten really long. I hadn't realized how much my cooking has changed over the last two years, since I started paying attention.