I first heard years ago that at In-N-Out Burger there were 'secret' off-menu items/preparations that could be ordered by regular customers in-the-know. I shrugged that off, however, because In-N-Out isn't a personal favorite of mine.
But the website Hack The Menu, which lists similar off-menu items apparently available at a wide variety of Americas largest fast food chains, including McDonalds, Subway, and Starbucks, intrigued me more.
That being said, a new review HERE of three of the Taco Bell off-menu items was a cold splash of reality. The Taco Bell employees were totally unaware of these 'secret' items, apparently, and, while game to prepare them on request, had to be handed a cheat sheet to do so. And in the end, the "Incredible Hulk" and "Superman" burritos seemed to me to be gut-busting ("extra potatoes, double portion of ground beef") mild deviations from existing menu items at more than double the normal price.