How much you keep is as often a function of laundry cycle as anything else. If you expect to cruise in area where you won't be able to do laundry but every two weeks, you either need enough clothing to last until you see a laundromat again, or things you can hand-wash in the sink with minimal water use. (Note that jeans are heavy & bulky & use a lot of water - we've had more success with medium-weight chinos.)
That said, it might be more effective to think about packing based on activities you might be doing, because its really all about your lifestyle. Clearing in and out of customs on many islands, respect seems to dictate at least long pants and a collared shirt. We each packed something suitable for a New Year's Eve party or clubbing (for me, a lacy top and shimmery pants - both washable). I've also got a brown pantsuit that I could use for a funeral or business meeting (luckily, neither of those happened in the last year), and an outfit that I can wear for something celebratory like a wedding or a shower. And, being a girl, after all, a little black dress.
All of these, hand-washable, non-wrinkle synthetics. For everyday wear: 4 pairs of water shorts, 8 T-shirts/Hawaiian shirts, 4 long pants, 2 pairs of nice shorts to wear walking around in a city, 2 sun dresses, 2 long-sleeve sunblock shirts, 2 turtlenecks, 1 sweater, 1 fleece sweatshirt, 1 long underwear, 1 complete set foulies, 1 fleece jacket, tennies, Keens (hiking sandals), sea boots, nice shoes to go with dressy outfit above.