You'll need layers during the Spring. It was warm to downright hot and sunny during the day...so Swimming Suits and shorts will do. However, a sweater or the appropriate coverage is needed for night. And DO NOT forget your flip flops!
Toiletries and Medical Supplies: Sunblock, Aloe, After Sun Lotion and lip goop!
Sandles, or some easy on/easy off shoe. You will need shoes to walk on the beach in. The sand gets very hot! If your going on just a relaxing vacation bring along different clothes. A pair of jeans, lots of shorts, some dressy clothes. Whatever. Or on the other hand, you might just see all the cute shops around and just have to buy new things for yourself!
Toiletries and Medical Supplies: Sunscreen, sunscreen, sunscreen. The higher the spf protection the better. Oooh, also lipbalm and leave in conditioner with sunscreen in them. Leave in conditioner works wonderfull for a day at the beach, It helps keep the tangeles out, and keeps the salt water from drying out your lovely hair. The lip balm helps keep your kisser from getting all burnt and dried out. Also, have condoms. You never know you, or your travel partner might need one. It makes more sense to me to have your own, than you know where and what they have been exposed to.
Photo Equipment: Underwater cameras. Those one time use ones are great.
Make sure you check what the weather forecast is before you go. The days were warm when I arrived, but the nights were a little cool and I wore a leather blazer a couple of times. If you're going in the winter you never know what kind of weather you'll get, so be prepared.
Toiletries and Medical Supplies: Pack your sunscreen! You're going to need it here, especially if you're fair-skinned like I am. Don't forget sunscreen on the top of your feet when walking around in sandals, I had lovely strap lines from them.
Camping/Beach/Outdoor Gear: Bring your swimsuit so you can lay around enjoying the warm Florida sunshine. And you might want to pack your own beach towel as a lot of the motels won't supply those. Or you could always buy one as a souvenir.
A chair for lounging on the beach is good as well, especially for friends who like to lounge with a beer ;-)
Luggage and bags: Forget your water wings? No problem. One block from the hotel is a place called 'Wings'. Really cheap sporting goods store with tons of bikinis, towels, flip-flops, and souveniers. Don't bother wasting your money at the hotel gift shop. I got a great reversible OP bikini for $25. Much better than the $50-75 minimum for the ugly suits sold at the hotel.
Bathing suit is essential for swimming in the warm aqua waters where you can swim close to dolphins if you are lucky. Casual but smart attire for dining and partying, something you'll find Ft. Lauderdale excells at.
Toiletries and Medical Supplies: Sunscreen for those coming from up north, the hot South Florida rays can cook you.
Miscellaneous: How many rich people can they pack on the waterfront of the Intracoastal.