I just got back from the Mexican Riviera, and we ran into the same problem. I only wore my shorts once, they were denim, so if I had needed to wear them 2 or 3 times, that would have been okay.
To save space, I wear a cover-up in port, over my swimsuit, rather than more shorts and t-shirts. The cover-ups can also double as a night shirt.
ALWAYS have a sweater that you can wear with your dress or slacks to dinner, and/or to the Clubs or on deck at night. I usually change into a sweatshirt and a pair of lounge pants....this time velour for the cold nights, usually the knit exercise type for the Caribbean.
I took only one sweatshirt with me, because I knew I would want to buy one from down there anyway, and I did. That's also how I've ended up with half a closet full of
DCL and island sweatshirts!
I do the same with the boys in my family...the cargo type pants that unzip into shorts. They're a lifesaver.
Oh....and on this last trip....I always wear tennies on the plane, with socks for when they make me take my shoes off. I hadn't packed any other socks, thinking I'd be wearing flip flops on the ship. At the last minute, I tossed in several extra pair of socks, and I am SO GLAD I did! I wore tennies every day but one. And the socks to bed, too, because my feet were freezing!