Part of this depends on the type of cruise: ours was through SE Alaska up through Glacier Bay and was an active adventure cruise on a small (62 passenger) ship. We got off every day and hiked, kayaked, took zodiac rafts up to glacier fronts, went through a bit of open ocean, etc. The trip was not fancy and relied heavily on water-proof gear. If you're on a larger ship, the fanciness quotient may be much higher ,esp. if you are not doing kayaking, etc.
I run cold so I took stuff to keep myself warm. I appreciated having a couple of fleece (one heavier and one lighter, wish I had taken 3) for layering; a waterproof gore-tex anorak; water resistant rain pants; tall waterproof boots; hiking boots. I also appreciated a billed hat, a fleece headband, waterproof gloves. Warm socks. Thin long underwear (like silk or polypro....I wore running tights). I wore running tops as t-shirts.I took a pair of winter-weight (fleece on the inside) running pants and enjoyed them. I also had a couple pairs of jeans but ended up mostly in running pants and tights under my lighter-weight rain pants.
Our expedition team sent us a detailed list of required and recommended gear (the tall waterproof boots were the required item; without them, they would not let us do zodiac shore landings because you stepped off the rafts into shin-deep water....This was nearly a deal breaker for me because I have super fat calves and it was almost impossible for me to find tall boots that fit...even men's boots didn't work because the calves were proportional to the foot size, but I did finally find a pair that fit skin tight but did not allow for any thing thicker than tights....no tucking in of pants, etc.)
At the last minute, I tossed in a black skort I got at REI and actually appreciated having something kind of "not gear" to wear during the evening with tights; I also wore it when we we had shore days in Petersburg and Juneau. The nights (although it never got dark) were cooler, exp. on deck when we were whale watching; and if the boat was moving, the "wind chill" could make things cold. I was in Anchorage about 20 years ago the last week of August and first week of September and it was clearly " turning over into fall." The first morning, it was 39 degrees, which was a refreshing shock from when I left Nebraska's 102 degrees.