While Jerry Seinfeld, Melissa McCarthy, Amy Schumer and Hugh Grant got top billing, sweet breakfast foods from the 1960s are arguably the real stars of the recent movie “Unfrosted^[1],” a comedy loosely based on the invention of Pop-Tarts.

What’s more, many of those breakfast products from the movie are still household names. When I was a child, I too enjoyed some of the sugary cereals featured in “Unfrosted,” and I...