Central Florida resident of four years here-late October in Florida is sunny, lows around 55-65 and highs around 70-85 with the occasional chillier day, moderate humidity, occasional rain and occasional hurricane.
Lots of good suggestions already, so I won’t pile on a ton, but my essentials are:
-more sun protection than you think you need. UV index is still high in the fall here, so don’t skimp on sunscreen. Get your ears and the part in your hair, too.
-something warm and lightweight you can jam in a bag/tie around your waist. I like an oversized flannel. Great for putting on the ground/ledges/benches to sit on during the day too.
-folding fan. I get them five at a time from dollar tree and always end up giving one or two away when I’m at the parks.
-hurricane plan. There’s no safer place to be in Florida than Disney for a hurricane, so don’t let the possibility stress you out. Just something to be aware of when booking flights/transportation that may be non refundable. The day before a hurricane is the best day to go to the parks since they’re usually empty, but you may have to be more flexible with your plans than you’d normally be if a storm does hit during your trip. It probably won’t, but just in case.
Other than that, the regular Disney trip essentials should get you by. Comfy shoes, comfy clothes, a bag that doesn’t drive you crazy, etc.
October is a great time weather-wise in Florida. You’re going to have a blast!