You should store the leftover potatoes in a sealed container. They will last 3-5 days in the refrigerator.  Reheat them by putting them in a large glass bowl and microwaving them for a minute or so until they are hot. You can also toss them in a skillet with a little bit of olive oil on medium-high heat. These are a few of my favorite containers for storing leftovers! Spend a bit of extra time to make sure they last longer in the fridge