Krusty-O's is a brand of the breakfast cereals endorsed by Krusty the Clown which prominently features his likeness on the box. The real KrustyO's, sold by 7 Eleven, were produced by the Malt-O-Meal corporation.
Krusty-Brand Cereal is the catalyst for the episode "'Round Springfield", when Bart swallows a "jagged metal Krusty-O" included in the box as a premium and is sent to the hospital. Later in the episode when Krusty holds a press conference to show that swallowing the jagged metal Krusty-O isn't dangerous, he immediately begins to gag before he is informed he swallowed a "regular" Krusty-O, which he claims must be "poison". At the end of the episode, another box of Krusty-Brand Cereal is shown with this promotion: "Flesh-Eating Bacteria In Every Box!", with Bart implying that he's planning to orchestrate another Krusty-O's-related lawsuit to replenish the $500 he spent on the then-recently deceased Bleeding Gums Murphy's sole album to give to Lisa.
In one episode Mr. Burns goes to shop and sees the Krusty O's and asks where the Burns O's are. Krusty then responds "they don't put nobody's on cereal boxes."