I'm not a fan of leftover ceviche. I know some recipes say you can keep leftover ceviche for up to two days. I find that the longer the shrimp "cooks" in the lime juice, it tends to turn chewy and gray. The lime juice also breaks down the vegetables after prolonged exposure. For these reasons, I recommend only making as much ceviche as you think you'll need in one sitting for best flavor and texture.