A crouton is a small piece of bread that has been fried, and dried. It is usually served on salads.
When Neelix was organizing a potluck in early 2375, Chakotay told Captain Janeway about it, and that he volunteered to bring the salad. Chakotay and the Captain were just getting over an argument, so she volunteered to bring the croutons. (VOY: "Equinox, Part II")