What should I wear? How cold/hot is it out on the ocean? Can I bring a backpack on board?

Hello Robbie, here's a link for you. https://www.channelislandssportfishing.com/what-to-bring

Yes you can bring a backpack, and depending on the weather for the day you go will decide what type of jacket, sweater,/sweat shirt, or if you need to do layers. Also make sure to take bottle water.

Ditto keller

Depends what time of year. In the summer a sweatshirt over your base layer would be fine. In the winter you will likely want to add a coat on top of that. You can bring a backpack on any boat.