Spooner, where are you staying? It sounds like somewhere in the upper west side (good).
We hit the islands every year, I just booked a surprise trip for our 15yr anniversary at the end of August at the Whaler on Kaanapali. She doesn't know, and I'm not going to tell her until a week before!
Oahu:
Honestly, unless you really want to go, avoid Hanauma Bay. The reef is dead and there are few fish. Much of the time, if there's even the smallest of swells, the lifeguard sit in the channels and don't let anyone else out in the deeper, better area. Waiting in lines to hit bad snorkeling just is sooo wrong IMHO. If there's no north swell, snorkel up at Sharks Cove and Waimea Bay.
Stop at Dole Pineapple on the way to North Shore, and do the maze. It's fun, then get some pineapple smoothies.
Shaved Ice in Haleiwa, and surf museum.
Go to Lanikai beach for relaxation. Voted one of most beautiful beaches in the world.
Maui:
One of the best things to do in Maui is beach hop. It's very easy to do on the upper west side, and you can often go where conditions are better for snorkeling. I'm going to paste some stuff from a doc I made I give coworkers.
From the Upper West side
Honolua Bay Best snorkeling on the island (in summer). Must go to, will want to go more than once. Go past Kaanapali and Kapalua. About 15 min north of Kaanapali, park on road, as close to gate as possible. Get there early (before 9 AM). Walk through gate, and through rain forest (pretty). Rocky beach, very little sand. If has been raining, may be a little murky. If not, 100 foot visibility. You can see conditions from overlook past the bay (great pictures). Snorkel to the right, towards a big boulder, then head up to the reef. Left isnt as good, but still nice. Tons of fish, eels, turtles. If theres a lot of water in the stream dumping into the bay dont bother snorkeling. If in winter will probably want to avoid: 15 epic right break with surfing competitions. Check conditions first.
Mokuleia Bay Part of Honolua, can snorkel around point to Honolua. Beautiful sandy beach, great to go to after Honolua. Park on road, walk down stairs. Good snorkeling too, sandy bottom.
Kapalua Bay Another great spot. Beautiful bay, restrooms and showers. Best snorkeling on right side of bay. Get there early, parking lot can fill up. Great for kids.
Honokeana Bay What weve begun to call Turtle Cove, just past Napili (see map above). Great spot for relaxing on the grass above cove, snorkeling with turtles is a guarantee!! Walk through Napili Point resort to grass area on north side of cove. Enter in lava step towards end of cove. If surf or surge, it may be too rough to enter. Try low tide
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North Kaanapali At Kai Ala Dr off Honoapiilani Hwy. (Old Airport Beach) Great facilities: showers, grass area to lie on, excellent beach. Surprisingly good snorkeling here, expansive reef right off the beach, lots of fish. Easy sandy entry just left of the restrooms. Tons of parking.
Black Rock One of the favorites on best beach in Maui, Kaanapali, at the Sheraton. Go into main Kaanapali, Sheraton (towards right, at the end) has a free lot of only around 10 spaces, can get if getting there by 8:30-9.AM. If full, can get valet at Sheraton (get a drink at the beach bars for validation), or park at Whalers Village and walk down. All facilities at hotel. Great beach side bar. Eat lunch or happy hour after snorkeling at The Hula Grill at Whalers Village.
Can jump off Black Rock, kids will like it. Best snorkeling out around the point. South Swell can mess it up though, make it surgy and sand in the water. But have had phenomenal snorkeling here, 80+ visibility out on point. Lots of turtles, eels.
South Side
Ulua Beach, in Wailea. By the Elua condos, parking lot.
Wailea Beach- at the Grand Wailea resort
Ahihi Cove Towards end of road, past Wailea. Marine preserve, can be a little murky
Tips Maui Dive Shop has free snorkeling maps. Theres one in Kihei, and Whalers Village, and Kahana Gateway.
Molokini boat trip that you wont forget. Visibility is 150+, when you get off boat its so clear youll feel like youre just going to fall right to the bottom. Two options: party boat right out of Maalea, its more expensive, tons of people. Barbeque, and drinks. Or, go through Maui Dive Shop, I think its only $45/person, gets there earlier and avoids the crowds. Will also go to another dive spot like turtle town.
The best restaurant on the island is Mamas Fish House, up past the airport near Hookipa Beach (Windsurfing capital of the world, always fun to watch from the overlook)
http://www.mamasfishhouse.com/
I dont know the south side that well, we always stay up towards Kaanapali or Kahana.
In Lahaina: All the restaurants are all right there on the main street, Front Street.
Kimos is pretty decent, its kind of in the middle of it all.
Bubba Gumps Shrimp Co is always fun and actually pretty decent. Its right up by the Hard Rock (fun for drinks).
Aloha Mixed Plate On the back side of the Lahaina Cannery mall, on Front St. Great for plate meals, and drinks. Next to Old Lahaina Luau.
Kaanapali: At the base of Whalers village theres the Hula Grill, and Leilanis. Hula Grill has always been a favorite around happy hour and dinner. Live Hawaiian music, great bar. Good food. Leilanis has Hula Pie for dessert.
http://www.leilanis.com/
Roys In Kaanapali now. Really good food there
North Kaanapali:
Dukes Beach House recently opened
Kahana: Maui Brewing, must go to for any brew lover. Right of the highway, turn left at Hoohui (McDonalds on the corner). In the Kahana Gateway Shopping Center.
Kapalua:
Pineapple Grill
Merrimans