FYI: Recently moved from FL after 11 years living there.
Fishing (for sport, collection or dinner) is HUGE down there. You will definately need to get a license to even collect, especially from brackish or salt waterways. They DNR down there patrols everything, and you WILL get caught. Be especially careful around the Everglades area and in the reefs. They are Nat'l and State parks, and very, very protected. There are areas you absolutely cannot take any flora OR fauna.
That being said:
Provided you have a license, you could try some of the following areas:
Lake Okeechobee area (South, near Sebring)
River and springs area (Mid North, near Ginnie Spgs/Ocala Nat'l Forest)
Wachiva and Econolachee (sp) River areas (Near Orlando)
Jetty Park (saltwater, Cape Canaveral)
Fish you might find worth collecting:
FL Flag Killies
Some types of Farowalla
Livebearers (Mollies, Gups, Platies, Vers)
You cannot remove mangrove shoots. They are protected in all of FL so be careful. Also, live rock and reef structures are heavily protected. Limit yourself to castoff shells from the beach.