Parts of Florida have been experiencing unseasonably cold weather this winter, so I'd wear a trench and cardigan on the plane. These will keep you comfy should the sun decide to hide on your vacation.
Theme parks are notoriously casual but that doesn't mean you can't look cute. And there are plenty of nice restaurants, bars and nightclubs to entertain grownups in the evenings, so if you plan on going out, pack a cute top and dark jeans or black pants for such occasions.
Here's some inspiration, click any outfit for details on the items shown:
Classic: A classic trench is a travel must-have that goes from day to night, sunny skies to thunderstorms. Red leather flats from the Gap are a comfy yet chic way to get around.
Casual Cool: I can't wear Converse sneaks myself (not enough arch support), but thousands (perhaps millions?) of people swear by them for comfort and hipster style. Add a boyfriend blazer to cover up if it gets cold.
Going Out: There's tons of nightlife in Orlando, both around the theme parks and even downtown. A pretty top and black pants is laid back yet still fun enough for partying.
Florida readers/travelers: What did I miss??