Preheat your grill to 350°F (if you can pre-set the temp on your grill. If not, just be sure to keep an eye on the packets as they cook). If you are using a fire pit, you will need at least 2 to 3 inches of nice hot coals to set the packets over. It’s also important that your fire pit has a grate to place over the coals.
Using a large mixing bowl, toss together the thinly sliced apple, brown sugar, granulated sugar, and apple pie spice. Set it aside.
Using a medium-sized mixing bowl, stir together the flour, brown sugar, quick oats, apple pie spice, and melted butter. Set it aside.
Tear six 10x18-inch sections of heavy-duty aluminum foil.
Scoop 1 cup of the apple filling onto the middle of the foil.
Scoop out ½ cup of the topping on top of the apple filling.
Fold the long sides of the foil packets together, then fold the ends toward the middle.
If you are using a grill, place the packets around the edges of the grill. If you are using a campfire, place the packets on the grate over the fire pit. Allow them to cook for 20 minutes. Remove the packets and allow them to rest for 5 to 10 minutes. Always be very careful when opening the foil packets.
Top the apple crisp with vanilla ice cream and drizzle the caramel sundae topping.