If you don't want to go, I'll take your place. (My wife has started packing in case you say yes.) (We haven't been on a cruise all year, though we did do 7 in the last 2 years.)
I book dives through the ship whenever possible. It avoids problems with the timing. In Beliize, the dive boat picked us up right at the ship at anchor. That way we did not need to tender in or out.
Don't bring a dive knife, you won't be able to get it through security when you return from your dive.
Remember all food is prepaid. Thus, if several things on the menu look good, order them all. On lobster night, order two tails and one prime rib right off the bat. If this is an freestyle dining cruise (I believe all NCL are), make your reservations right away. That avoids out of space situations later on the cruise. Also, aim for 8:00 dinner. It is late enough to get everything done and to shower and get ready, but gets you done in time to see the show which usually starts at 9:30 on NCL. The entertainment is outstanding.
Bring a water glass (plastic) and coffee cup with you. You will find that you eat breakfast and lunch at the buffet. I've found the cups are too small and that I need to take 6 cups of water/ice tea just so I don't need to refill during my meal. Same for coffee.
You may want to bring a piece of string and a small nail with you. The ship uses shipboard credit cards for everything that requires money (alcohol and gifts). These also open your cabin door and are your boarding passes/id. My family likes to poke a hole in the card with the nail and then hang it like a necklace with the string.
I like to put a piece of duct tape on my cabin door or on the wall nearby to make finding my cabin easier.
Use the shower by the pool to wash your scuba gear. Its easier than trying to do it in your cabin and is much less messy.
You will have a great time unless you want me to go in your place.
(My wife has just finished packing in case you do.)
