What clothes to wear in Florida in September?

Comfortable clothes that you can layer: Since the weather remains warm, you should still pack T-shirts and shorts so you're not too hot, but it would also be wise to pack at least one pair of leggings, jeans or pants. ...
Ponchos: If you're going in September, ponchos are a must-have.

Is it okay to wear leggings in 80 degree weather?

They come in different colors and different styles, just like shorts do. You should not wear leggings in conditions where temperatures exceed 80 degrees Fahrenheit (27 degrees Celsius). Too much heat can cause your skin to break out and can make you feel uncomfortably warm, especially when you start to move about more.