Besides making this yummy baked spaghetti, there are lots of ways to use plain leftover spaghetti. It can be refrigerated for three to five days, or frozen in resealable freezer bags for a month. To refresh, bring a pot of water to a boil and submerge cooked spaghetti for a minute or two. Drain and serve immediately with your favorite sauce. More ways to use leftover spaghetti: make an easy summer pasta salad with chicken; try a baked spaghetti pie (from Spends with Pennies); chop it into shorter lengths and add it to stir fries instead of rice, or add to chicken noodle soup.