When you buy portabella mushrooms, look for firm, moist caps that are not broken. They will hold for approximately 4 to 5 days after purchase when properly stored.
The turkey and sausage stuffing can be made up to 3 days in advance and stored covered in the refrigerator. The mushrooms can be stuffed and assembled on a cookie sheet the day before. Top with cheese and bake the stuffed mushrooms right before serving.