I’ve been making my own breakfast cereal for about 30 years.
The basics haven’t changed, it’s mainly rolled oats and toasted sunflower seeds, but the other ingredients have gone through several variations over time. The current formula is two lbs rolled oats, two lbs toasted sunflower seeds, a half lb peanuts, and a a half lb walnut pieces. All unsalted, of course.
And I toss in whatever combination of bananas, strawberries, and/or blueberries I happen to have on hand.