Step 1: In a medium bowl, combine the thinly sliced apples, brown sugar, flour, cinnamon, nutmeg (if using), and vanilla extract (if using). Toss gently until the apples are evenly coated.
Step 2: Unroll the refrigerated pie crusts. Cut each circular crust in half, resulting in 4 half-circle pieces. Alternatively, cut into 6 equal squares or rectangles if preferred.
Step 3: Lay out 6 sheets of heavy-duty aluminum foil (about 12x12 inches each). Place one piece of pie crust onto the center of each foil sheet. Spoon about 1/2 cup of the apple mixture onto one half of each pie crust piece, leaving a small border for sealing. Place a small pat of butter on top of the apple mixture in each packet.
Step 4: Fold the other half of the pie crust over the apple filling, forming a half-moon or pocket. Crimp the edges with a fork to seal the pie crust shut.
Step 5: Bring the edges of the aluminum foil up and over the pie packet. Fold the top edges of the foil down several times to create a tight seal. Then, crimp the side edges to ensure the packet is completely sealed. For extra protection against tearing, double-wrap each packet in a second layer of foil.
Step 6: Cook the apple pie packets over medium-low heat. If using a campfire, place them on a grill grate over glowing embers or directly into the dying embers (avoid direct flames). If using a charcoal grill, place them on a grate over indirect heat. If using an oven, preheat to 375°F (190°C) and place packets on a baking sheet.
Step 7: Cook for 15-25 minutes, flipping the packets halfway through, until the apples are tender and the crust is golden brown. Cooking time will vary depending on the heat source. For oven baking, cook for 20-25 minutes.
Step 8: Carefully remove the campfire apple pie packets from the heat using tongs and heat-resistant gloves. Let them cool for a few minutes before opening, as steam will be hot. Serve warm, optionally with a scoop of vanilla ice cream or whipped cream.