Welcome aboard, Lisa! I'm excited to hear that you're looking forward to a magical cruise with Disney. It's a great idea to fly in the day before, just to ensure that even if you encounter flight delays, you'll still arrive in plenty of time to board the ship.
Many guests do buy a one day pass or a one day Park Hopper pass for the Walt Disney Resort to use the day before they cruise. However, there are not half-day passes available. If you don't think you'd have enough time in the parks to make the ticket worth the cost, then another option is
Downtown Disney, where no admission is required. There is so much to do and explore there, you could be busy all day! Or if you stay at one of the Walt Disney World resorts, you'll have a fabulous pool to enjoy throughout the day as well.
Disney Cruise Line offers ground transportation from both the airport (you can always choose to stay at the Hyatt inside the airport), and the resorts at Walt Disney World to Port Canaveral. Though there is an additional $35 per person each way cost to this service, I promise you that it is worth every single penny, as Disney takes care of all of the details. This really makes the transition from land to sea and back again seamless and stress-free.
I hope that helps as you continue to plan, Lisa! I'm happy to help if you have further questions before you set sail!