With regards to your clothing ... I'd suggest staying away from anything cotton, at least for your tee shirts. Cotton pants (like jeans) may not be a good choice either. Cotton, when wet, takes a long time to dry, and you'll feel miserable (and colder) if you've got cotton clothes on. Look into convertible pants which are nylon ... they can be found in most outdoorsy stores like REI, EMS, Gander Mtn, etc. (look online too at Campmor). WalMart and Target sell a polypro tee shirt for under $10 (short sleeve) which works well with layering. I'm not sure if they have the long sleeve ones though but again, check online.

Most importantly ... get off the boat as much as possible!! Alaska is best seen when you're not on a floating hotel!