For clothing: You never need as much as you think.
Two things I never leave home without: 1) a long black travel dress like they sell at TravelSmith or Lands' End and 2) black high quality (non hiking shoe looking) sandals that also support enough to wear as walking shoes [Ecco, Clarkes, etc.].
I found that a good quality pair of sandals (black) that can double as walking shoes works great. The sandals can be paired with the travel dress for evenings that require a more dressed attitude. And the dress is light enough to air while hanging during the day and/or can be rinsed in a hotel sink and drip-dry.
Also bring cheap $2.99 flip flops for the dive boat (they crush in your bag fine). And sneakers/gym shoes.
2 bathing suits (one to wear, one to hang dry) in black or navy what can do double duty under a gauzy shirt or denim shirt while site seeing or at night.
khaki shorts are acceptable almost anywhere as long as you pair it with a clean non-emblem T-shirt or bathsuit with long-sleeve shirt.
Undies and non-underwire bras: get some that have a cotton/lycra mix. You can rinse in sink and drip-dry at night or bring many pairs as they crush down in you bag. Also get yourself a travel-brick. TravelSmith and such carry 3 sided zipper squares that are mesh. You can cramp them full and zip up the "un-mentionables" and have no fear if you bag is opened or has to be opened as they wont spill-out.
I DO NOT us a wheeled bag for a carrying on regs and computers or cameras as over booked flights or ones in which you have to "hop" to an island will almost always require you to check all bags at the gate, even after they didn't take the bag at regular check-in. Put you change of clothes and things you may need right away in the wheeled bag, as the last-minute checked bag will be on the tarmac when you land. Put the reg and computers and camera in a purse-looking or brief case which they will allow you to put under the seat in front of you. This way they don't get banged around in the last-minute check-in.
As for marked bags: I always get extra insurance for my dive large bag which doesn't has a dive flag on it, but does say "Mares". And I put those little luggage lock on it. My husband use to work for the airlines. He says the large locks scream "Valuables!" and your bag will undoubtingly get on a later flight. The little ones are a nuisance to any luggage handler riffling through bags and will go for the unlocked ones. Large wheeled duffles are so common now, that they don't scream for attention.
Have fun on your trip --Starfish