I'm pretty sure it started by reading the sides of the packages when I was a kid. Riboflavin, I discovered, was Vitamin B-2! Niacin, Vitamin B-3!
So, I was quite excited to find out that Sunday was the 100th anniversary of breakfast cereal. On February 19, 1906, William Keith Kellogg incorporated the Battle Creek Toasted Corn Flake Company. He and his older brother, Dr. John Harvey Kellogg, while working at a Battle Creek sanitarium, accidentally invented the process for making cereal flakes. W.K.'s company, of course, became Kellogg's.
Personally, I like to mix my non-presweeted cereals. They must differ by grain and by shape. Cereal generally comes in Corn Oats Rice Wheat and is shaped like a ball flake oh pellet square (or rectangle)
So, among popular cereals: Cb- Kix Cf- corn flakes Cs- Corn Chex Oo- Cheerios Rp- Rice Krispies Rs- Rice Chex Wf- Wheaties, raisin bran Ws- shredded wheat, Wheat Chex
So, if I start with a Ws, say Spoon-Sized Shredded Wheat, I can add an Rp, an Oo, and/or a Cf, e.g., but not a Wf (because it'd be two wheat cereals) or Rs, because it would be two squares.
I don't mix pre-sweetened cereals, as I recall Rory and her friends did on Gilmore Girls. Some of the sweetened cereals of my youth have changed their names. Sugar Smacks are Honey Smacks. Sugar Pops are now Corn Pops.
Happy anniversary to the breakfast cereal. It is another reflection of the effectiveness, of the power of advertising, especially in the television era - "K-E-double L-O-double Good, Kellogg's best to you."