You have to bring I.D . when you get to the ship, they will keep your passport. make a photocopy, or just bring a drivers license. Its to get back into the ships terminal area when you need your i.d. (not actually when you are walking onto the ship).
I am sure during excursions, they will tell you what to do with your valuables. just bring the bare necessities.
Tenders will run all day long during days at port if tendering. usually you can catch them every 15 minutes- or depending on how long the tender ride is.
When you get off the ship, you are usually bombarded with lots of tour guides. Some are private, and you can sign up right there. But going with the ship, is a good idea. IF a tour is late coming back to the ship- the ship knows about it..... and wont' leave without you!
p.s what ship are you going on??