Regarding snorkel stuff, there are many places that rent it also. I think Boss Frog and Snorkel Bob are 2 of them. If you plan to use it other times, then buying may make sense, but there are places right off the beach you can snorkel without going on a tour, so you may want to have it the entire time you are there.
When we drove from Kahana (on western coast of Maui north of Ka’anapali) we headed north so we were on the right side of the road, which was away from the cliff. When we became concerned about safety and narrowness of the road there was nowhere to turn around and we were just relieved that we didn’t meet someone coming the other way. It was exciting and beautiful, and nerve-racking.
So it sounds like the road has not changed and may not be a good choice.
If the weather is bad, like it was on our honeymoon, get on a plane and go to Kona on the big island. Its always sunny and great snorkeling.
Snorkel Bobs told us they don’t rent the new style full face masks to snorkel with because they are dangerous, and the last several drownings were with people wearing those. Something about making them panic and they’re heavy? Anyways, keep that in mind, don’t rent those even though they look appealing.
We brought snorkeling gear which allowed us to use it wherever. We went to the Big Island first and both there and on Maui snorkeled places where there were no rentals. Cost-wise, i think it was cheaper to bring than to rent more than a few times.
Don’t buy snorkels at Costco; sorry, they are just not the same quality. Folks who do not like to snorkel have not tried the right gear. If you plan on going to HI a few more times, buy your own mask and snorkel tube (Snorkel Bob’s signature masks and fins are great). They don’t take up much space in the suitcase and are not heavy, but the right mask makes a whole lot of difference compared to cheap plastic gear. Especially makes sense to buy for folks who wear glasses like Mr. B - his mask has optical glass that is pretty close to his prescription. Then rent fins on the spot. I also highly recommend getting neoprene socks for wearing with fins to prevent blisters from rubbing. They also help protect your feet while getting into the water if the shoreline is a bit rocky (don’t try to walk in fins!).
Our last trip, as a family, to Maui was when our D and S were in high school and middle school. We loved the snorkeling - trip to Molokini Crater and off Black Rock at Ka’anapali. They loved taking surf lessons near Lahaina. We all enjoyed the Old Lahaina Luau. My kids did not like the Road to Hana - it was just too much time in the car. It was lovely, but for us it was not the best day. (They still refer to it as the Road to He-double toothpicks.) When D asked where we should go for my decade birthday this fall, I said I would love to go back to Hawaii. I will be reading here and will grab a copy of Maui Revealed.
@xpd600090, Happy Travels!
DH and I went to Maui several years ago.
Highlights:
Snorkeling at Napili bay. There were sea turtles. We were staying there so we did this more than once.
Road to Hana. We took our rental car all the way around. The suggestion to bring food is good. We stopped a ton. We stopped and watched surfers on the north side of the island. We saw so many beautiful things on that drive, especially some side road through a neighborhood we read about in a book. It went to the coast and it was one of the most beautiful places I’ve ever been. I didn’t love the curvy road with vegetation on both sides and the occasional waterfall. I really loved the back side of the island on the section of the road past Hana—the “don’t take your rental car” side of the journey. I don’t usually break rules but this was worth it It was so different and remote. I felt like we had to endure that curvy jungle bit to get to the good stuff. I have found I prefer beaches to jungles. We also saw the cutest herd of cows! It really did take all day. We did have food with us but by the time we got back to civilization we were so tired and hungry we stopped and ate at Panda Express!
Dinner at Humuhumunukunukuapua’a at the Grand Wailea at sunset. It’s open to the outdoors and there was a luau going on next door so we killed two birds with one stone, sort of.
Most visitor deaths in Hawaii are from snorkeling. Most of the deaths occur in shallow water. If you’re going to snorkel, you should be an experienced swimmer. Don’t snorkel alone. http://www.civilbeat.org/2016/01/stand-up-or-die-snorkeling-in-hawaii-is-a-leading-cause-of-tourist-deaths/
Biking down Haleakala is dangerous as well. People have died, broken bones etc. https://www.tripadvisor.com/ShowTopic-g29220-i86-k7293888-Biking_down_Haleakala-Maui_Hawaii.html
If you want to get to the summit of Haleakala for sunrise, you’ll need a permit. They need to be reserved in advance. https://www.nps.gov/hale/planyourvisit/permitsandreservations.htm They can be reserved 60 days in advance, but I see some available starting March 9. I was surprised to see some available.
The problem with going places that are prohibited with your car rental, yes I said prohibited, they don’t just say we don’t recommend, is if you do run into trouble, you’re on your own. There’s no tow trucks or ambulances nearby. You could be waiting hours. If you do damage the car, congratulations, you’ve just bought yourself a car. Because you violated your rental contract by taking it where they said you couldn’t, your insurance and their insurance won’t coer you. There’s plenty of places on Maui to explore without going where it’s prohibited.
I’m not even going to get into Maui Revealed. Let’s just say the series is called the “Reviled” series in Hawaii for a reason. Many of its recommendations involve trespassing on private land.
There are plenty of activities that a family can enjoy without putting life and limb at risk, trespassing or violating contracts. I moved to Hawaii (not Maui) because it’s the most peaceful, beautiful place where I could move permanently. Enjoy.
If you’re taking a snorkeling trip with a tour company, then they will give you a vest, which keeps you afloat and warm(er). Also, they have those pool type “noodles,” which act as floatation devices. And of course, the tour operator employees are certified lifeguards. IMO, there’s very little risk of being hurt or death, especially with 100 (?) people in the water with you.
I’ve also had and seen zero problems in the sunrise ride down the mountain in the couple times that I’ve done it. Just take your time going down the mountain. It’s a curvy road.
Just remember, people have died in car crashes, but we all still drive cars. And trains, and planes.
Definitely agree with Bunsen about not buying snorkel gear at Costco. Uncomfortable! Snorkel. Bobs will fit you to something perfect. It’s easy to keep it an extra day and drop off many places. I’m a bad swimmer, so they rented me something to put around my waist for flotation. It helped a lot as far as comfort in the water. My husband did mock me and ask if I was going to get arm floaties and rubber duckies, though. 
We travel with our own mask and snorkel and borrow (rent) the fins, as they’re bulky and heavy. I did notice on my last trip that several snorkel places rent for a week as well, so that might be an option.
We are certified scuba divers but we like to snorkel, too. I’m always surprised at the number of people in our group who have never snorkeled before and are now going to do it in very choppy waves! Yikes. And even when there are a lot of people in the water, it’s easy to get separated so that no one notices a person in distress.
Our snorkeling trips were all canceled in Maui due to rough water. That’s why we went to the big island 
Lots of people at the hotel were injured while swimming due to the unusual weather.
On Kona there is a hotel with a protected bay and great snorkeling. That + a mai tai is plenty of excitement.
Last time I was in Honolulu someone drowned – i think it’s fairly common for tourists who are unfamiliar with swimming in the ocean to have problems.
Not saying don’t go – just don’t assume you’re invincible.
Wow, I didn’t realize snorkeling could be dangerous. Thanks for the warnings. We’ll keep that in mind.
WATER can be dangerous. One thing that people don’t realize is that seemingly innocuous water can have treacherous currents that can pull folks far from where they expect. If they expend all their energy fighting the current, they will have no energy to try to get back to land. The ocean is NOT a bathtub or swimming pool and needs to be respected.
Snorkeling is fun - just respect that you need to follow some basic safety precautions. I make my crew travel in pairs, and keep an eye out for each other. Don’t go on your own if the surf is too rough on you feel uncomfortable with the waves, etc.
If you take a tour, let the guide know you’re a little uncomfortable, and they will help you out. The first time my kids snorkeled we were in Maui, and they were 9, 11, and 13. We hired a professional oceanographer (Ann Fielding - she was great) to tell us all about the fish, drive us to a good spot, and snorkel with us. At first the 9 YO was nervous and wore a flotation device, but within about 20 minutes he was going under water.
If you’re going to snorkel, you can’t beat Hawaii.