Cruisetour #6 and shorex questions??

[chloes nana]

I am booked on the Zuiderdam crusietour #6 for 8/14/10. My question is: do you need to book all your additional shore excursions that you may want to add on or is there a way to do this as you go on the land tour part?? I am really confused about this whole thing, I know some tours are included, but I also see alot of open excursions at almost all stops?? Is it worth booking them ahead or is it just as easy to fly by the seat of our pants and buy as you go? thanks!!;)