No excursions shouldn't be a problem. You'll enjoy wandering in Nassau a bit.
Castaway Cay can be done for free without any problem. We did rent floats for our kids ($6 each), which they enjoyed immensely.
Bringing wine onboard is fine -- Disney allows this. When we were waiting to board, we saw them loading suitcases (happened to see our own suitcase going onboard), and I understand why they don't want liquids in there. They take all the suitcases and throw them together in big canvas roller carts. If yours happens to land on the bottom, a wine bottle wouldn't stand a chance. Most people have soft-sided luggage these days, so you could potentially hurt your own clothes and those of others.
As for bringing wine into the dining room, this is the HEIGHT OF TACKINESS. Have a glass in your room, if you wish, but I think it'd be terribly embarassing to walk into the restaurant with a glass in your hand. It just isn't done. Remember you'll be seated with other people at your table. The waiters certainly will notice -- probably no one would say anything to you, but they sure will say something later! You don't have to have alcohol at dinner at all.
As for pictures, well, that's my weak spot -- I'd cut out souveniers and alcohol first, but that's just my priority. Do remember to bring along extra batteries and plenty of digital media (or a laptop for downloading).
Even if you love soda, the mug isn't really a good deal. Remember, you can get soda three times per day in the restaurants -- the mug is only useful BETWEEN meals. You can bring your own sodas onboard much less expensively. If you really, really want the mugs, you can book through
AAA and get them free.
Don't worry about souveniers. I was surprised that they didn't really have much I wanted in the ship's stores. Something I find highly ironic: Now that I'm able to afford more stuff, I find much less that I want. When I was young and poor, I always wanted stuff I couldn't have.