If you are travelling to Florida you will probably be thinking of hiring a car. Since January 2013 you not only need your national driving license with you, it is also strongly recommended that you carry an International Driving Permit with you.
International Driving Permits were made compulsory in the state of Florida on 1st January 2013 which meant that if stopped without having one on your person you could face jail or a mandatory court appearance. However in February 2013 the Florida Department of Highway Safety and Motor Vehicles has said this law will not be enforced until the Geneva Convention on Road Traffic can be made. While the law cannot be enforced currently, it does still exist so the AA strongly recommends that you carry one with you.
You cannot apply for IDPs more than 3 months before travelling abroad so keep an eye out for changes in the law before you travel which may affect whether you need one or not. There are lots of other countries that require or recommend carrying an IDP so do your research before you pick up your hire car!