Probably sandwiches. Considering he wasted 2 all-powerful wishes on sandwiches. TWO. The one with the maze, and the one with prismo. He could wish for anything he wanted, so what does he wish for? A sandwich. Luckily prismo just made him one so he could use his wish for something better, but that's beside the point. The point is sandwiches.
In many episodes, he has also said that he very much likes spagetti.