When are you going? Where? What do you plan on doing?
For me I lay out the whole time by the pool. I go with bathing suits and sarongs as my "day wear". I don't carry tshirts or shorts or anything. However there are tons of inside activities too and in my opinion it is cold inside. I'd bring a hoodie or something. Of course obviously an Alaskan cruise would be different. If you are going Mediterranean, only Americans wear shorts. Something like what you have on in the picture would be perfect. If you are staying farther north, Bahamas Bermuda things like that in the winter, you'll want to have a jacket. I was in Bahamas over New Years Eve cruise and it was chilly. It was great and warm at the other ports but Bahamas were about the same temperature as Florida. In Hawaii, if you are going up the mountains (like to the top of the volcano) it will be cold yearround up there. If you are going horseback riding on an island, you'll definitely want longer shorts (Bermuda or capris) to save your legs. You want to bring really good walking shoes as a lot of places have a lot of walking.
A week long cruise usually has 2 formal nights. You'll see some people in prom gowns, especially on a more expensive line. Carnival tends to not dress up so much. But still think high school dance--did your high school have a girls ask guys dance? a semi-formal winter fest or something like that? That type of attire will be the average. The other nights are more casual though most people will be in dresses. Think maxi dresses, sundresses, things like that. Like I said you will want a jacket/shawl as the dining room can be cold.
Please add more details so we can be more specific or write me. Without knowing what month or to what countries, it's much more difficult to tell you what clothing. The outfit you have on in the picture is great for the days on a cruise.