Sunscreen is a must
Pack as lightly as you can. You don't want to die of heatstroke lugging a lot of clunky bags or suitcases. Besides you can buy almost anything you would need if you forget an item. In general, unless you are coming in stormy weather
or December thru early March, you will not need a lot of warm clothes. A simple first aid kit is a good idea. There are some areas where Jellyfish and Stingrays are encountered. It seems more common around Marco Island and Naples, but they are around every beach. Bring a lightweight digital or quality "aim and shoot" camera if you are just looking for shots of the beach or pictures of family and friends. That should be adequate. It gets hot lugging heavy camera gear around in 98 degrees. I don't know WHO in their right mind could stand camping out in muggy 80 degree nights in a tent, but people do it here. If you do, I would definitely take precautions against
Mosquitoes and other pests. Choose your spots with care. In general, the weather is subtropical with
the possible exception of December thru early March. The dry season is generally from November until early June. After that there WILL be a Thunderstorm almost every afternoon. Have an umbrella during this period. Suncreen is extremely important
because an hour on the beach here is about like six hours on the midwestern beaches.