Clothing is obvious, but if you are going to be away for three months consider the variety of activities and weather you may have. Pack clothing that you can layer and make sure that you have something for the beach, a lounge at home day, a chilly day, a rainy day and a formal dinner. Appropriate footwear for each will be necessary. Bring back up swimwear, a hat for the sunny days and a light jacket just in case.
Beach towels are a must. Protect yourself with sunscreen, a face moisturizer with SPF and a lip balm with SPF. Make sure that you have a beach umbrella that can screen you from the sun while you are not in the water. Having a cooler is helpful when you want to bring some refreshments for the beach.
A small first aid kit that you can keep in the car always comes in handy if there is a little accident on the beach. Make sure you bring a bag of emergency items just in case you are not feeling well on one of the days of your trip. You may include some over the counter medication for a headache, stomach upset or diarrhea. This will prevent you from having to find a pharmacy in a place with which you are not familiar.
Make sure that you have your camera, your camera plug, backup batteries and an extra memory card for the camera. Saving the memories of your special vacation is an important part of your trip. Document the special moments, the sunrises and sunsets, scenery and any unusual wildlife that you might experience.
Make sure your cell phone and charger are in your bags. If you need your laptop, bring it, but make sure that you use your time wisely and unplug. You may want to bring your favorite DVDs for the nights that you stay in or on rainy days.