Leftovers were what remained of foods that had been prepared and eaten earlier.
In 2371, Neelix served leftover gabosti stew, as he hadn't gotten around to making the lunch special yet. (VOY: "Elogium")
Later that year, when asked if she had enough food to feed Tolen Ren, Tom Paris and Harry Kim, Lidell Ren said she could add some leftover rolk to the stew. (VOY: "Ex Post Facto")
In 2372, Harry Kim asked if Neelix had any leftover pleeka rind casserole, as he wanted some for breakfast. The Talaxian was sure he could find some. (VOY: "Scientific Method")
In 2374, the thermal array in Neelix's kitchen wasn't working, causing Neelix to worry that the crew of USS Voyager would have cold leftovers for dinner and would blame him. (VOY: "Deadlock")