Remember Man vs. Food, host Adam Richman would travel all over the country looking to take on food eating challenges that offered prizes and glory to anyone who completed them. It goes way beyond "can you finish this pizza in an hour?" But I'm not sure I ever saw Adam or current host Casey Webb take on a cereal eating challenge.
The first time I heard of or saw a Whataburger was in the 1994 movie 8 Seconds. Luke Perry played bull rider Lane Frost and in the scene, Lane takes his girlfriend Kellie to the restaurant on a date. I can't remember the conversation but he asks "are you going to finish your 'Whatachickn'?" My interest was piqued in overdrive.