When I was a kid, we thought it was _the_ neatest thing that Kelloggs and Post (and General Mills?) offered six-packs of miniature single-serving cereals, all different types in one pack. It was a real treat when our parents brought home one of those packs.
You had to lay the little box down flat, tear open the top on the dotted line, cut open the waxed paper bag inside with a pair of scissors, and pour in the milk. It was great. Those little boxes were so special. The “single serve” boxes were also available at some coffee shops. Do they still have them? I saw a mini-cereal box display at the coffee shop at the old (demolished in 2010) Transbay Terminal in San Francisco.
I remember those too! My parents used to buy them for treats on camping trips.