Ah, the everlasting big vs small travel pack debate. I've gone both ways and found that it entirely depends on your travel style and both ends of the spectrum can be taken to extremes. But, we've settled into a 45 L carry-on backpack each supplemented by a small day pack for daily stuff like a bottle of water, snacks and a place to carry that jacket you don't need in the afternoon.
We used to carry a standard suitcase full of everything we might need. But over time we found we didn't need half the stuff we took and got really tired of lugging a heavy suitcase down narrow streets, onto crowded busses wrestling it around small hotel rooms and a couple times, having to return to airports to retrieve lost checked baggage. Now we just take carry on packs, but, we tend to travel budget style to lass touristy destinations. On the few occasions when we go to a single destination we don't worry about weight and bulk too much.
Also, as we travel more we buy less "stuff" - just lost interest in souvenirs and T-shirts in favor of just taking photos and experiencing whatever place we end up at.
As for the rest - we have compact snorkels and masks which fit in our carryon (but no fins - too bulky). If we take a book, we donate it when done and pick up another. Our clothes are quick-dry synthetic blends (wool + synthetic) which nowadays are pretty comfortable and even good looking. The days of floppy pants bulging with cargo pockets is gone - unless you want them - now there are good-looking, good fitting pants and shirts made from synthetic blends. Underwear? Ex-Oficio quick dry shorts and undershirts - wash'em out when I take a shower - they're dry within the hour and ready to go. Every week or two we'll do a regular machine wash of the clothes. The only thing I haven't been able to totally ditch are cotton T-shirts - just have to bring a couple of those.
Yeah, I occasionally miss the trusty old jeans or cotton underwear, but not enough to push me into a larger pack in order to carry them.
Here's an article on where we've evolved to so far as packing is concerned http://imaginetraveldiscover.com/2014/03/31/204/#more-204
