When we got to Orlando the day before the cruise, it was 40 degrees and raining. I thought, Gee, why did I even come here? It's like being at home.
Port Canaveral was a bit nicer. Probably sixties and sunny. When we left port, it was very windy and quite chilly. I refused to use the pool that day (and I'm not a big swimmer anyway), but I used the pool every day after that, sometimes twice because of the heating. Disney lists the temperatures of the pools on one of their TV channels, so I know it was always in the 80s.
When we got to Nassau, though, it was a complete turnaround. We had been watching the weather, and we saw high sixties, low seventies. But we were lucky, and the forecasts were wrong. It was at least high seventies.
Castaway Cay? Eighties. It was perfect.
That being said, I'm spoiled with the heated pools. The water at the dolphin swim was *freezing*, but it wasn't shallow. The water at Castaway Cay was warmer, but still too cold for me. I'm one of those weenies who gets crampy feet if the water's too cold, so I didn't spend much time in the water.
I was really paranoid about what to pack, because I'm *always* cold. So I packed a lot of everything. On the islands, I wore very, very light pants, t-shirt, and a light zipped hoodie, so I could de-layer as it got warmer. On the boat, I dressed warmer, because everything is air conditioned. Jeans, courduroys, hoodies, long-sleeved shirts. But remember, I'm always cold. Other people walked around in shorts and t-shirts even out on deck and were fine.
My recommendation would be to pack for everything. Bring some warm stuff, bring some cool stuff, and bring some heavier things for nights out on deck. If you're a naturally warm person (Texans usually are

), you should be okay with whatever you pack.
But I will tell you this-- my fiance, who is one of those "I don't need a coat" people, didn't bring a sweatshirt and found himself quite chilly on deck anytime we went out (especially at night or when we were moving). He will make sure to pack one this time!
The last time, we stayed at Disney the night before, but it was because we had free passes to Magic Kingdom from a rained out Halloween Party. We rented a car to drive from Disney to the port, and then we took Disney's transfers from the port to the airport. Renting a car for two hours was forty dollars (because I didn't fill the tank with that 1/4 gallon I used), and the transfers would have been seventy-something for the both of us, so it worked out well.
But if you're staying at a hotel near the port, they have shuttles that'll take you there. You'll just need to get transportation from the airport to the hotel or rental agency.