Maui Snorkeling Gear
If you plan on snorkeling in Maui you can rent equipment on a daily basis for $5-$25 a day based on the quality of the gear. This is a good option if you are only planning to snorkel 1 time on your trip (or future trips). If you plan on snorkeling many times or on later trips, you should get equipment suited to your needs.
When buying a snorkel set (mask,snorkel,fins) it is best to get one with a dry snorkel and short fins. Since you will probably be traveling a compact set with bag would be the best bet. While you may loose some quality and features, travel sets will work just fine. You can also find sets designed for the kids (make sure they come with a dry snorkel). Below are my choices based on price and quality.
Snorkel masks are full face masks with a built-in dry snorkel. A dive / snorkel mask can be used for scuba as well as snorkeling. you can also purchase a prescription dive/snorkel mask for eye glass wearers. The full face masks are good for snorkeling in calmer waters with many models having a camera mount. I prefer a dive mask so I can use a longer dry snorkel. This allows me to snorkel in choppy water or as I swim. If you are an eye glass wearer like me you will want to get a prescription mask. They come in -6 to +6 , so call your eye doctor to get the proper strength before ordering.
A dry snorkel has a special valve on top of the tube that completely seals out all water (and air) when a wave comes over, or when you dive underwater. That way you don't have to clear them when you come back to the surface. A longer model will allow you to swim in choppy water while snorkeling. Higher quality snorkels do a better job of keeping water out while under water.
Fins (flippers) are shorter for snorkeling than for scuba diving. You can get fins with straps or or full foot. With full foot flippers you don't need diver socks. I prefer the straps used with dive socks so I can still have feet protected while walking to shore. It is important to have the right size so the fins do not fall off easily. With straps make sure to take extra straps in case you loose one.
Dive socks / boots are made of neoprene with rubber soles to protect your feet from rocks and lava while getting in and out of the water. I prefer the socks as they are usually a little thinner than boots making it easier to use with my strap flippers. Boots are thicker with heavier soles and designed more for scuba diving. The sock or boots can also be used for hiking through rocky shores, lava and around tide pools.
Unless you are a poor swimmer you do not need a vest when snorkeling in Maui, as the water is naturally buoyant. Dive vests are great for poor swimmers and long swims when you just want to rest. They quickly deflate and inflate so you can dive underwater. Most snorkel tours will require you to use a life vest (usually one of their bulky standard vests) but will allow you use your own dive vest.
You have plenty of options for taking pictures underwater. The best option (and most expensive) is a Go Pro camera. They are very durable and create great photos and videos. Many camera companies offer great underwater products that can get good results. While image quality may suffer, you can purchase underwater housings for your smart phone. Just be careful to follow instructions so you do not flood you camera/phone.
Other Useful Items
Here are some other useful items to have along. If you are kayaking or just want a dry space to put your clothes, keys, etc. use a waterproof dry bag. Waterproof phone cases are inexpensive and work great at protecting your phone and key fob. Anti-fog mask cleaner works great for clear viewing although diluted baby shampoo works just as well. Maui passed a law which requires all suntan lotion to be made with reef safe chemicals.