We're going on Independence in November. We've been on Freedom before. Only Oasis class and Quantum class give you the option to book shows beforehand. So for smaller ships, including Independence, you can just show up.
Even if Windjammer is done with lunch, they re-open for dinner, but there is also Sorrentos and Cafe Promenade which will have small sandwiches, sweets (cake/cookies/pastries) and Fish and Ships on the pool deck is now included except the Lobster I think.