I say book ahead also - which I did. It got the money part out of the way prior to the trip. However, I held off on the floatplane due to my fright of it. I was encouraged to do this when we reached port by fellow mates - and I thought - they won't have any available and I can say - couldn't do - all sold out. However in Ketchikan I walked off the ship and got a flight (one of the last two seats available so they told me). If you are not like me - it will do you well to book ahead or you will miss an awsome flightseeing adventure. And others that took the helecoptor tours truly had a great time.
Hope this helps.