Does the cruise come with a luggage allowance i.e. you get to ditch your luggage so they look after it, or do you have to lug it round the cities with you?
If the former pack a small hand luggage bag to get you through the first 3 nights, then repack for the final 3 for the way home and take whatever you want. I would use packing cubes so everything stays organised.
Assuming the latter in which case the above will be inconvenient:
I'd take dresses that can all be used for day and evening if you possibly can, and I would then wear them for two evenings and then a day or two.
If you prefer culottes do you also need the skirts? Will you end up not wearing dresses etc if you prefer them for sightseeing? If you won't wear the dresses cut down to 3 total.
If you prefer culottes I would add another pair and remove the shorts and skirts.
Cut the number of tops down to one per day you expect to wear them.
Take a cardigan/jumper and a hat if you want it.
Shoes I would take one trainer, one comfy walking sandal and one pair for by the pool.
I've just done 17 nights away and I took: 5 dresses, 1 pair of trousers, 1 pair of shorts, 4 tops, a jumper, a swimming costume, a pair of leggings and I think that was it. I did one wash 5 days through and it was fine.