Thinking outside the box.
Post a package to the hotel well in advance, surface mail, cheapest rate.
Put in batteries, chargers, dive lamp, toiletries, Fins, booties, etc.
Pack it with teeshirts, underwear etc.
Put in everything thats heavy and you could replace if it got lost in transit.
Check that the parcel arrived before you leave so you know you dont need to take these things to the island.
When you leave the island post it back home or donate it to charity.
Camera Gear
This is very tough
For 1 week you can live without the laptop.
Buy a palmtop / organizer and a couple of 8gb memory cards, copy from your camera to the organizer daily.
Batteries for the strobes, can you buy them there? It will be expensive but then you wont need to carry them and a charger or see above.
Next I would limit the topside luggage I would take on that leg. Tropical climate, relaxed atmosphere.
So 2 changes of clothes, 2 tee-shirts, 2 shorts etc, wear one, pack one, and wash as required.
No spare shoes etc.
Empty wash bag then add only what is absolutely essential.
Have small bottles / tubes of anything you need, leave all the rest.
1 shampoo enough for 4 washes, small toothpaste, small suntan lotion, etc. That stuff is heavy.
If it is not absolutely essential dont take it.
Next Dive Gear
Do you need a wetsuit, would a dive-skin do the job, or rent one there.
Rent fins, they will work equally well for a week.
Do you need a backup mask, if its prescription yes, if not then you can borrow or rent one if needed.
Rent a light for the week, that saves carrying it and the batteries.