You are certainly welcome to attend the
Chip & Dale Campfire at Fort Wilderness. There is no admission fee or entrance ticket needed for this experience. There is, however, a minimal fee for marshmallows if you would like to do some roasting. (You can also bring your own.)
The campfire consists of guitar music and songs, followed by an outdoor showing of a Disney film. The independent website The Mouse for Less, usually posts the Fort Wilderness movie schedule. Go to their site at themouseforless.com. On the left, under "trip planning", click on "Walt Disney World." Then scroll down to "recreation" and click on the "Fort Wilderness Campfire Movie Schedule" link. If you don't have access to a computer or would like to decide while you're at WDW, you can go to the guest relations desk at any of the theme parks or the front desk of your hotel. They can call Fort Wilderness for you and let you know what movies will be playing during your visit.
You can also ask the front desk of your hotel to verify the time of the Campfire during your visit, as this does have some variation based on what time it gets dark.
Enjoy your stay at Walt Disney World.