It can be quite hot and humid out at sea so better bring sunblock (it's difficult to find or buy any from Hanoi's pharmacies), mosquito repellant and a wide-brimmed hat. The sunblock will come in handy should you swim or ride a kayak.
Miscellaneous: If you'll take an overnight cruise, bring along your own bottled water. Your boat might provide you a couple of complimentary bottles but that might not be enough for you. You can of course order on board but water and all other drinks cost extra.
Clothing/Shoes/Weather Gear: We travelled from HCMC up to Hanoi in March and the only time we needed to wear a jumper was in Dalat at night, and when we were out on Halong Bay. So I would suggest that you bring a jacket or jumper that you are not terribly fond of. Then you can dispose of it by giving it to a local. I donated mine to an elderly chap who was wheeling his grandchildren around the Hoan Kiem Lake in Hanoi.
Luggage and bags:
Small overnight bagpack with one day change of clothes, swimming gear
Toiletries and Medical Supplies: Bring your own toiletries - No shampoo, toothbrush and toothpaste provided. They do give you a towel and provide toilet rolls.
Mosquito repellent (usually at the deck of boat, you will feel that there are some mosquitoes around)
Photo Equipment: Lots of memory cards for taking landscape of Halong Bay
Miscellaneous: your favourite book, a deck of card
Toiletries and Medical Supplies:
You need not to deliberately avoiding sun light when you’re visiting Ha Long Bay. If you do, your holiday destination should not be Vietnam at all.
I’ll encourage you to do some sun bathing after 3pm and do remember to apply sun block or you friend may wonder whether you have been visiting Africa destinations.
Another great companion for sun block is none other than cans of chilled beers (at least that work for me).
The winds get biting cold during the months of Jan and at night, it can plunge down to as low as 5-6c. Brr! On top of that, there were light rains. My red parka which I wore in Scandinavia came in handy. It ward off the rain and kept me snug.
Haha, did I ever mention that I got this Landsend parka at half price because this is actually a kid's size sweater? Check out www.landsend.com for their nifty parkas.
Toiletries and Medical Supplies: No need to bring toilet paper. It ain't the dark ages here.
Photo Equipment: Bring lots of memory sticks or compact flash. I doubt you'll find a digital cam equipment store in Cat Ba. Alternatively there is a camera shop at Ha Long City, right at the harbour front selling film.
Miscellaneous: Hmm, maybe a cap for bad hair days..
Bring lots of magazines when you're touring on a junk in Ha Long Bay, if not, you'll just plain go out of your mind with boredom!
Haha, Ken, you are right, I did lug around this girly mag everywhere. Should have brought a fake moustache to smoke on one of those pipes.
Toiletries and Medical Supplies: I've thrown up in the water two times in my life, once while snorkeling in Puerto Vallarta, and another time while kayaking on Maui. I was determined not to let this happen to me again, so I got the patch. Scopolamine was release into my skin behind the ear. It lasted the three days we were on the water, and it worked!
Bringing a good camera to Ha Long Bay will definitely make you a happier & proud traveler. My pals were amazed of those formations by looking at photographs. I am definitely more blessed than them because I was in it.
Ok, gigabytes may be too much but no harm having few hundred MB for Ha Long shots.
For those who’re using compact or 35mm SLR cameras do bring enough films of different ASA reading. When you’re out of films, no one can really help you.
May be the boat man do sell some films or you may try drink vendors at those caves?
Luggage and bags:
Not many people come to Ha Long with heels and beautiful outfits. We normally dress simple and with our backpacks on our back, especially true for those who sign up for 2D/1N or 3D/2N package.
I check in my excessive baggage at hotel which I going to stay in before I fly back to Kuala Lumpur at no cost. Of course they would like to keep your baggage as ransom so that you will revisit them. To me, that is fine too and we actually exploited each other for our own benefits.
Luggage and bags:
A backpack or a day bag
Clothing/Shoes/Weather Gear: Swimwear, shorts, sunblock, sunglasses, sandals...
Photo Equipment: You may need to clear up the space in your digital camera, cos you will take a lot of pics!
Miscellaneous: Mosquito repellent