If you are going on an all-dive vacation, I find that you don't need too much in the way of clothes i.e. you don't need 7 days of wardrobe changes for a weeks trip.
\I usually pack 2 swim suits, 3 pairs of shorts, 6 t-shirts, sandals, and underwear (which takes up the most space).
I usually wear khaki pants and a long sleeve sun-shirt (one of those covertable ones which can have the sleeves rolled up and buttoned down), sneakers/gym shoes and a sun hat and jacket.
I wear all the bulky items, except the many day changes of underwear and socks.
Pack the underwear in one of the new packing cubes or in one of those plastic bags you roll to get out the air. This saves a ton of space.
I pack it all in amongst my gear to cushion it and check the big roller bag of clothes and gear.
I take my regs, mask, toiletries, and a swim suit on the plane. If they lose or delay my bag, I can still get a rental BC, weight strap, fins, etc.
So pack light in clothes (you can always rinse out stuff in the hotel or send it out for cleaning) and use those rolling plastic bags or packing cubes to take out the air in the undies!