Shake Shack and its investors are not the only ones gaining from its debut on the stock market. While investors gobbled up the stock valuing it at $2 billion, hundreds of New Yorkers feasted on free burgers outside NYSE after its stock, priced at $21, jumped to almost $50 and closed at around $46. Most content of all, however, seems to be founder Danny Meyer. Having raised $105 million through its IPO, his stake was last valued at $342 million. Not bad for something that started out from a food cart.