It really comes down to what kind of photos you want to take. If you want photography of the streets and shops in st. Thomas you might find a 35mm way too long. If you're shooting birds on the same island, you'll find a 400 on the same island too short! I think it all depeneds on your goals. If your goals are to take some snapshots to remember the vacation then pack a G7X or RX100 ii/iii. If you want professional quality photos, then bring professional gear, and accept the burden that comes with carrying it. Bouncing flash inside a cruise ship is completely doable, but will get you some looks for sure. Not using a flash and using something like your 35L will yeild a lot of shots with properly exposed, motion blur free, poor lit photos.
The last cruise I took I brought my 70D, 50 1.4 and 18-135 STM. I found off the ship, I kept only the 18-135 on and in many places it was both too narrow or too short for the shot I wanted. Now, don't get me wrong it got 80% of the shots I wanted, but there were some on both ends I'd want wider or longer. Additionally, there were shots I wanted to take with a tripod and long exposure, but I didn't bring one. However, I don't regret not bringing a longer lens in the least. I don't regret not bringing my 10-18, but only because it wasn't released then. I actually was shopping for a UWA in St. Thomas and found out the prices weren't anything close to special and the selection sucks.
If I were to do it all over again, I'd likely buy and bring either a RX100 iii or a G7X. I could have gotten 80% of the shots I took with either of those and had a lot less camera hassle.




The ship's engine may cause issues with sharpness.


