Annap - what the boy says to Scrooge's instruction to buy the turkey is "Walk-er!" - and Scrooge replies "No, no, I'm in earnest." [I'm quoting from the first ed. of 1843, which was well enough followed (in this respect) by the film.] Anyway, in the dictionary of vulgarities "Lexicon Balatronicum", 1811, we get the parent expression, "Hookee Walker", "An expression signifying that the story is not true, or that the thing will not occur." In other words, it's an impolite version of "Get lost!" or such.