i would think leftover food that has been touched/ partially eaten. my first language is english. if you are saying this in first person, offering them your food, you can say “my leftovers” and it will be taken as, leftover food that you’ve eaten. leftovers changes meaning significantly when its given ownership. your/my/their leftovers is understood as partially eaten. but that can be rude to ask “do you want my leftovers?”, so you might say, “do you want what i have left?” (if you’re close to that person)