Avoid having leftovers, if possible. If you do have them, use them again.
Leftovers can be used for other meals very easily. There are no limits to how creative you can be. Here are a few examples: make fruit purées or smoothies with bruised fruit, make soups with leftover vegetables, turn old bread into breadcrumbs, make a sandwich with leftover fish or meat, or prepare a salad with cooked potatoes, pasta or rice.
Here are some recipes to inspire you: