A Hamburger Today. As in: "I'll gladly pay you Tuesday for a hamburger today."
They recently did some serious work for us as they deduced how to make your own Double Double from In-N-Out Burger. They went to the trouble of ordering burgers from one of the west coast stores, had them overnighted, and then deconstructed the classic. You can read about it in The Burger Lab: The Ins-n-Outs of an In-n-Out Burger.
And if you want to make your own Double Double at home, they even provided a handy recipe.
Image source: maubrowncow (Flickr)