Hi B Jacobsen. Is this the 31-Day Hawaii/Tahiti/South Pacific
cruise from San Francisco to Tahiti?
Laundry shouldn't be a problem. As Penny mentioned, there are self-service laundromats on board--plus, Princess also has a laundry service for a charge. If it's anything like we had in the past, your clothing will come back pristine. (They even pressed our blue jeans!) So, I'd pack enough for a couple of weeks, and have laundry done about midway through the cruise.
There will also be plenty to do on sea days. As you will be crossing the equator, look for the special ceremony to commemorate the event. I'm sure there will be other activities such as movies, lectures, live shows (we had a pianist on one long cruise, for instance), and of course the casino!