If you've ever made homemade granola, you've probably noticed that it starts out crisp and crunchy, but often loses that crunchiness after a few days, especially if it contains dried fruit. (The moisture in the fruit softens the oats.)
To keep it crisp, freeze the granola in zippered storage bags; it'll keep for up to six months. Freezing will also prevent the nuts in the granola from spoiling. Let the granola come to room temperature a few minutes before serving.