I spent three days on Santa Rosa island in July 2015. I used one of the charter boat companies (Island Packers) to get there - they were great. Upon arrival, expect to haul your gear a 1/4 to 1/2 mile for even the closest campsites - but it's absolutely worth it. Some folks had gear carts, but we packed light enough that it wasn't a problem. It is absolutely important to understand that the Channel Islands isn't your usual campgrounds, it's an island with protected species that are all over the place. The Island Fox is the biggest wildlife challenge I've encountered. They are friggin adorable and very numerous (you will see dozens, if not hundreds if you stay for a day), but if they can't steal it or eat it, they will pee on it. Understanding that, it's very cool to hang out in the campground watching them interact with the campers trying to steal food. Use the "fox boxes" to store all of your food and stuff you don't want peed on and you're good.

The beach is nearby and offers great snorkeling in kelp beds, we saw numerous rays cruising nearby and got many great photos. Depending on your interests, sea kayaking, stand up paddle boarding and the like are all possible.

The island has numerous hiking trails that take you up the surrounding "mountains" that overlook the island for fantastic views. Part of the island is off limits as part of a wildlife refuge, but I never felt like that prevented us from having our fill of wandering around on the parts that were good to go.

Overall Santa Rosa is a fantastic place to visit and make sure you give yourself enough time to see what all the island offers. An afternoon visit would only give a small taste, it's well worth staying for a couple days.