I was born and raised in Manatee County, so I have endured the summer heat for many years. During that time I have learned tips and tricks to still be able to enjoy what Florida has to offer. The most important step is to plan and ensure you have what you need to safely enjoy your outdoor activities.
The most important step is to be properly hydrated. This starts before you even leave your house. I recommend starting every day with a large glass of water. When you first wake up you have gone 6 - 8 hours without consuming any liquids. This large glass will get you caught up and on the right track. You should bring enough water for everyone to last the entire day. On a day in June or July, I bring a minimum of 16oz of water per person, per hour. If you are doing a physical activity you may want to up this amount. I like to freeze a portion of the water the night before and put them in a cooler to help keep them cold during the day.
The next important item is sun protection. Make sure you wear proper clothing that will protect your skin from the sun. You should also wear a brimmed hat and sunglasses. You should also use sunscreen and reapply using the manufactures directions. I personally use Aveda's daily light guard brood spectrum sunscreen. In Florida's bright sun it doesn't take long for you to get a sunburn. I also recommend utilizing shade or a portable tent to help keep your area cool.
Lastly, don't overdo it. If you start feeling tired or overheated go inside and take advantage of some air conditioning.