Hemingway had extensive coctail experience and used it in his writing. What a charachter drinks and how he fixes it gives the reader insight into the character. If Hemingway had contempt for a type of drink, he put it in the hands of a charachter he wanted to reader to feel contempt for. If he enjoyed a particular drink on Pilar, he put it to the lips of a boating protagonist. If he thought a cocktail sophisticated or complicated, he served it to a character when he was worthy of it. Before To Have and Have Another, I never really considered character development revealed through drink.