The odds are that a Florida summer is going to be VERY rough for you; you will have to take steps to prepare for and combat it. I grew up in the Louisiana delta, where believe it or not, the humidity is WORSE than in Florida. Here are my extra tips that not many people have mentioned:
1. ALWAYS walk on the shady side of the street if there is one (which there will be, except right around noon.) If you are driving, put a shade in the windshield and cover the steering wheel and any carseats before you leave the car; they can get hot enough to burn your hands. (Be especially careful with carseats; kids have been badly burned by hot buckles.)
2. From noon to 4 pm, plan to be indoors or under water. (Noon to 2 is not that bad, but 2-4 is the hottest part of the day.)
3. Always prefer lightweight woven clothing to knitted clothing; it dries much faster, which cools you more quickly and reduces the chances of chafing. Stay away from synthetics unless they are the sort specially made for sports performance, such as CoolMax. I agree with the other posters; light colours only.
4. Sunglasses and a wide-brimmed hat help immensely; plan to wear them at all times when outdoors. (I recommend Watership Trading Co. hats; they are great. Pricey, but worth it.) I also second buying a misting fan and making sure you have enough batteries for it. Get the kind with the wide opening; ice helps.
Carrying a cloth for wetting down pulse points is good, too. If you carry a ziploc with you, any vendor with ice will give some to you for cooling purposes, even the fan kiosks.)
5. Carry spray-on wide-spectrum sunblock, and use it about once per hour. (It really doesn't have to be spray, but spray is easiest, and you'll do it more often if it is easy.) UV-B rays literally cook your skin as they beam down on you, and good sunblock actually makes you feel cooler as it blocks that. If the surface of your skin feels hot, you need more sunblock.
6. Most importantly, know the signs of heat exhaustion and seek first-aid help *immediately* if you start seeing them. Healthy people DO get heat exhaustion, and if it is not treated FAST (within about 30-45 minutes) it can progress to heat stroke, which can kill in minutes. This page has a good clear description of what to watch for:
http://www.mcare.org/healthathome/heatexha.htm
Now that I've frightened you to death, have fun! (Seriously, if you prepare for the worst you will be a lot more comfortable. If you don't prepare, adverse reaction to the heat is likely to make your vacation a lot less fun.)