Soon, these and other ageless spokes-characters will get a new neighbor: Pringles, which Kellogg is buying from Procter & Gamble in a $2.7 billion deal expected to close this summer.

What’s Pringles, the world’s best-known stackable-chips franchise, doing in Kellogg’s bulging portfolio of cereals, cookies, crackers and such? The answer sheds some light on the way Americans are eating these days, and on what ails Kellogg, whose shares have lagged the market in the period since March 2009, when the Standard & Poor’s 500-stock index bottomed out. The S.& P. is up 115 percent over that time, while Kellogg is up 59 percent. And the company’s operating profit is basically flat — at $1.95 billion in 2008, and $1.97 billion in 2011.

“We’re not happy with our performance the last couple of years,” says John A. Bryant, who became the company’s chief executive in January 2011. Mr. Bryant, 46, whose looks would be described as all-American were he not from Australia, is sitting in his office one March afternoon, discussing some unhappy trends for a few of the company’s biggest products. Products like Corn Flakes and Rice Krispies, whose sales dropped in the last year. Those brands, not coincidentally, are also the easiest for makers of private-label cereals, breakfast’s version of generics, to knock off. So Kellogg and its 400 food scientists, engineers and technicians are cooking up new products at a frenetic pace — new cereals as well as new categories of food and flavors for what everyone here calls “snacking occasions.”

“Here I am, sitting in this office, and in that building, right there,” Mr. Bryant says, pointing to a plant just a few blocks away, “is one of the few private-label cereal plants in the U.S., probably creating 200 million pounds of cereal a year. Because that thing is there, we have to keep bringing new foods to consumers and delighting them, because if we stand still, people catch up.”

Americans might not be buying Corn Flakes the way they did a decade ago, but they love a good snacking occasion, and shoehorning a few more Pop-Tarts, Nutri-Grain bars and Special K Savory Herb crackers into our day is a core mission for the company. But the real growth for Kellogg, as well as for packaged-food rivals like PepsiCo and its Frito-Lay division, is in snacks in foreign markets, and that is where Pringles comes in.