Costco! It is located right by the airport, so it is easy to fill up right before you return your car. You do a lot of driving around the island and we ended up filling up on the way back from a day trip to Paia and again before we returned our car. Gas prices average from $3.10-$3.90.
Please follow The Snorkel Store (blue and white seahorse logo) on Instagram. They post a daily snorkel report for 3 different beach locations across the island, North West, Ka'anapali and the South Shore. They rate it between 1-10 and describe water conditions, visibility, waves and wind. Please check this daily before going out and always be aware of water conditions, they have very strong currents and shore breaking waves, PLEASE BE SAFE!!!
The Snorkel Store! Located in Lahaina near the resort area. This is always our first stop, best store for snorkel gear, they are very helpful and will give you a map of the island.