My husband and I were at Princess Cays on 11/4 and had a cabana. I reserved it online. There was an envelpoe in our stateroom when we boarded the ship that had all our excursion tickets for the week in it, including one for the cabana.
When we arrived at Princess Cays, we simply took the ticket(and our float tickets)to the float stand and gave it to them. They had an attendant that walked us to our cabana and set it up for us. They did give us a little wooden "Cabana Pass", but no one else seemed to have one. The lady at the float stand seemed surprised I had it when I returned it.
I hope you have as great a time as we did. I can't believe we this time last week I was there!!