I still remember as a kid walking down the cereal aisle and looking for which cereals had the best toys. That was the entire basis for how I chose cereal at that age.
I was also exposed to another strange aspect of cereal marketing: the sugar content. My father instituted a rule that we could have any cereal with <= 10 grams of sugar per serving, and so my sister and I became acutely aware of said levels. Captain Crunch was out of the question, but Cinnamon Toast Crunch would dip above and below the line, with a period of several months. Nearly all cereals I watched displayed this behavior.
I said, "I like to add sugar to my rice crispies" and she said, "You couldn't add enough sugar to your rice crispies to equal the amount in the frosted kind."
And now, it's hard to buy even adult cereals without sugar in them. They are all so sweet. It can't be good.
Ah, I love a good challenge!
The cereal, once you eat it, is gone forever, but the toy will last until you lose it/get bored of it/your dog eats it. Since your parent was buying it, it was like getting a toy for free.