it was our first time going to catalina island. it's an absolutely be-a-utiful island. depending on the time of year, here are some to-do's while visiting catalina.
i HIGHLY recommend renting a golf cart and driving around town. this is how the locals get around town and it's definately the easiest and cheapest way to see great views of the island. when you get to town, there are a few places to rent and they all charged the same, $40/hour. However, some will offer an incentive like pay for 2 hours, 3rd hour free......
they'll give you a map of different trails like certain view points and the botanical garden.
there is a small exhibit ($5) off the casino that has many pictures and history of the island. did you know marilyn monroe (norma jean during this time) lived on catalina before she became famous?
you can also take a tour ($20) of the casino that was built as catalina island was being developed. there is a G-I-A-N-T ballroom and movie theater.
and of course, being on an island, there's snorkeling, kayaking, parasailing, glass-bottom boats and more. :)