Hello Jessica, welcome aboard! I just returned from the 6-night sailing on the Magic out of Galveston and would have loved to have stayed those two extra nights! You're going to really enjoy your 8-night cruise with Disney!
On your 8-night sailing out of Galveston on the Magic, you can expect to have the following attire rotation for dining in the evenings, (although this is always subject to change, the following is most likely):
Night 1: Cruise Casual
Night 2: Formal Night
Night 3: Cruise Casual
Night 4: Cruise Casual
Night 5: Cruise Casual
Night 6:
Pirate Night
Night 7: Semi-Formal Night
Night 8: Cruise Casual
On Formal Nights on the ship, I've seen anything from tuxes for the men and evening gowns for the ladies, to just a shirt and tie for the men and a simple summer dress for the women. But, my opinion is the dressier the better! When else do you really get to be all dressed up? Plus, it makes for some nice photo opportunities. So, pack some formal wear, Jessica, and have a wonderful experience on your cruise!
Let me know if you come up with any other questions before you set sail, as I'm always happy to help!