Joanne,

You can book excursions, both complimentary and non-complimentary, once on the ship. The danger is that a particular excursion may be sold out. Most of the reports this year were that most passengers got the excursions they wanted whether they booked precruise or on the ship. Some people reported that they booked online and then canceled and rebooked on the ship. This resulted in a refund of the amount paid for their online booking. The cost of the excursion was placed on their shipboard account so that shipboard credits could be used to pay it.