The ScubaLuv dive shop in Avalon runs a boat called the King Neptune. It is almost always 3 tank diving at 3 different sights.
In general, they have a good system to handle quite a few divers, (up to about 25).
No guide goes into the water, but everyone gets a breifing on where to see stuff and what to expect.
The typical scheudle is to meet at the dive shop at 0830, leave the dock close to 0930. Diving might not finish up until around 1700.
It's a good, spacious, fast and safe boat that can handle the crowd very well. They have a make-your own sandwich bar for lunch and plenty of drinks.
Equipment: Rent your gear at the shop when you check in. You'll need a 5-7mm wetsuit.
If you go to Avalon on Santa Catalina Island and don't want to stay on a beach, in the water or shopping around, try golfing. Yes, on perhaps one of the oldest golf courses in California, 1895, it now is an executive 9 hole course of 2,100 yards with par of 32. The Catalina Island Golf Club allows public useage of the course and you can get in 18 holes with the double set of tees. The best part is that there are few players during the week and getting a tee time is easy. Call ahead and reserve.
Equipment: Bring your clubs with you over to Avalon or rent them at the Club House. Golf cart rentals for course. Check on type of shoe to wear when reserving time.
Your on your little Island and you want to get away from it all. Too many tourists yakking up a storm and disrupting your tranquility. What to do? Get out on the ocean away from the maddening crowd and kayak your way to peaceful bliss. The best place to do this is away from the crowds to begin with and that is to walk past the Casino and go to the Descanso Beach Ocean Sports location at Descanso Beach Club.
You will find that there are tours as well as on your on kayak journeys. They will make sure that you know all there is to know about paddling your Madeline around on the waters off Catalina. They also have snorkeling gear to rent out by the hour or half day. I have snorkeled the Descanso Beach area and must admit the giant Kelp beds are a bit scary to maneuver around.
Equipment: The best part is that all you need are your casual beach wear. All equipment is provided by the company.
The underwater park is a beautiful shore dive. You can easily walk there from anywhere in Avalon - but bring a bag with rollers if you are taking your own gear. If it's a weekend or the summer, they will probably have tanks and weights down at the Casino (where the dive park is) for $20 + air fills after your first .
Equipment: For gear rental, I recommend Scubaluv.