Consider:
Dramamine
Calling your MD for prescription med
Getting an amidships cabin if it's not too late if you do not have one

I agree that a cabin low and midships is a good idea.

DH has had good luck using meclizine, the generic version of Bonine.

How likely/unlikely is seasickness when you're on an Alaska inside passage cruise? We're thinking of having a balcony cabin on Lido or Aloha deck, toward the front of the boat. Thanks! H is getting better about not getting seasick but has had that slight tendency.

Atropine patches probably are the best bet. Some side effects, but better than sea sick. Beware Compazine and similar drugs. Generally safe, BUT significant potential for really bizarre, dramatic and exciting side effects. Also some of these drugs can be had over the counter in some countries. Names usually end in zine.
I almost got sea sick in the Gulf of Alaska. Not at all rough but big, slow undulating waves.

Thanks for all these ideas. I posted also on Europe site and got some good answers there as well.