None of this is as hard as it sounds. I started making my own cereal because I found that store bought granola is just too sweet. I stretch it with raw oats and then add nuts and seeds for extra nutrition. I have a collection of glass jars I got out of the trash years ago. I put everything in a jar and shake it up good. My mix lasts twice as long and keeps me full almost the entire day.
I started making yogurt when I found out how easy it is to do. I never bought a yogurt machine either. Waste of money. Don't need it. Just heat up some milk in a big pot. You can dissolve some gelatin in it if you like firmness. Let the pot cool down until the milk doesn't burn your finger when tested. Then stir in a cup of plain yogurt, the kind with live cultures like Dannon. Wrap the pot in towels and place in a warm place. I sometimes put it out on the driveway when it's sunny, or you can set it on top of a radiator or other heating unit. Like bread it needs a little warmth for the bacteria to grow. Once it's cooled down completely put it in the ice box to firm up some more. Add fresh fruit for sweetness and save on money and calories.
Trail mix is another good DYI project. I don't like raisins, they're too sweet for me. I use craisins instead. Most of the time I can buy the ingredients for my trail mix, peanuts, nuts, seeds, chocolate chips and other dried fruits for a lot less than the mix would cost. I pack up small bags and a can for the car. I always have snacks to keep me out of Mickey D's.