This is sure a touchy subject...as many have different opinions,
but I will express mine and contribute to the board here.
I enjoy getting dressed up each evening, as I have not worked in
over 12 years (I am 38 and been on over 29 cruises)and I sit in
the house each day. So to me, it is pleasureable and nice to
be "dressed up." My husband dresses each day six days a week
and his idea of a vacation is to be relaxed and comfortable. On
formal evenings he does wear a dark suit but changes into docker pants and a short sleeve collared shirt right after dinner.
On the past few cruises, I have noticed men not even wearing a jacket....not many but some. I have noticed men wearing light colored suits and pants with sport jackets....so I guess you can say its ones choice. On European cruises, people tend to dress much more formal on such evenings. During the summer on caribbean cruises people are more informal on formal evenings.
One does not see many men in tux's unless you cruise on the more upper cruise lines such as Seaborne cruises or the Sea Goddess....
I also noticed on the many cruises I have taken, the first formal evening is more dressier than the second.
My son also doesn't feel comfortable to dress in a suit (he is soon 12) and I don't want to buy a suit for him to wear twice in one week then put it in his closet and find it next year small on him....so what I do, is buy him a black pair of docker pants and he will wear a long sleeve dress shirt with a tie. Both father and son after formal dinner changes into casual clothing.
As you can see, everybody is different.....but my suggestion is that you probably don't want to feel "out of place" so I would take along some kind of a jacket, dress shirt and a couple of ties if you do not want to bring along a suit. You can change after dinner....