French fries are a terrible thing to waste, but leftover fries typically aren't very good. When you try to nuke them, they usually come out soggy or stale. To restore fries to their original glory, try sautéing them instead.
Picture: Hungry Dudes
One Good Thing recommends adding a thin layer of cooking oil to a skillet and heating it over medium high heat. Once it's hot, toss in your fries in an even layer. Cook each side until fries are a crispy, golden brown. Blot excess oil with a paper towel, add some seasoning and get ready to stuff your face with fries.
As an alternative, you could also grill leftover fries in an oven. I haven't tried that method, but this one worked well for fries I reheated over the weekend. They were perfectly crispy and delicious.
If you want more detail on the sautéing method, head over to the original post at the link below.
The Best Way to Reheat Leftover French Fries [One Good Thing by Jillee]