As most people know, when you go to In-N-Out Burger there are a number of common "off menu" orders you can place, such as 4X4 and Animal Style. What I'm discovering now however is that this culture of menu items for those in the know extends to other chains as well. For example, at most Starbucks here in the North Los Angeles county you can order an "Undertow". This is a shot of expresso with a pump of vanilla, in which they then cascade a large spoonful of heavy cream, folding it in so that curls into the bottom without mixing. You then immediately shoot it down (just like you would a shot of alcohol). The duel sensation and flavor of the cold cream and the warm sweet espresso is awesome.
I have also heard that Jamba Juice has an "employee's menu" with a collection of drinks that aren't on the menu (one being called a Starburst or something like that) though I haven't tried any of these yet.
Does anyone know of any other popular off-menu items at the various chains they visit?