Luggage and bags:
Bring with you a backpack, but also you will find the compulsary daysack a handy thing, for trips to the beach, shopping and the such.
Clothing/Shoes/Weather Gear: We went in Summer (June/July) which is 'Rainy Season' where they get tropical storms. So be prepared to get wet. Saying that, it only rained a few days of the 6 weeks we were there.
And it was still hot!
Miscellaneous: Don't forget a hat - you'll probably find that you need one.
Depending on what you taste like, you might get bitten loads or not at all.
I never got bitten once, and I slept with windows open, no net or repellant. My friend however, was eaten alive despite sleeping in a closed room, under a net and soaked in mozzie rep!