Here's two for the price of one.
As we have discussed in the past, Kellogg's sponsored some of Hanna-Barbera's earliest shows. That meant the stars would be doing in-show ads for various cereals.
First, Quick Draw McGraw (Daws Butler) is filming an ad for Rice Krispies. Eventually, after Kellogg's ended their association with H-B, Snap, Crackle, & Pop would be brought to animated life.
Then, Hokey Wolf (Butler again) schools Huckleberry Hound (Butler) on how to shill for Corn Flakes.
Hokey never got his own show, but H-B used Phil Silvers as inspiration for Top Cat, and, a decade later, Butler recycled his Hokey voice for Hair Bear, while Arnold Stang was cast as Top Cat, largely to avoid TC & HW sounding too much alike.