My favorite spot is right in front of WKORV. There is a park there called Kahekili Park (since you won't be able to use the WKORV facilities) that has bathrooms and showers. I just saw Robert's response pop up - Kahekili=Airport Beach. The reef is quite good. Black Rock is nearby and while it isn't the greatest snorkeling, it is a bit more protected from currents - at least before you get out to the end - and it is a good back up on surgey days. There is usually a turtle hanging out there, and we even saw an octopus last year. Black Rock is my go-to for beginners because it is a very easy sandy entry and because so far, we have seen a turtle every time. It is very crowded though.
Down south, there are very nice reefs at Ulua Beach. It is my favorite when we are staying in that area. Lots of fish (saw a manta there once) and beautiful coral, but since you are staying in the Lahaina area, I wouldn't make the drive unless you want to see different areas while you are on the island.
Honolua Bay is another popular area. We went there on a boat so I can't comment on parking or shore access, but I know it can be done. It was a beautiful area.
We've been to Molokini 4 or 5 times. We used to take one of the boats that did a 7:00 trip, back by 9:00, before our return flights, lol. I love being out on the water and it was fun to go, but as far as fish count, I was always disappointed. YMMV.