You may get seasick even if you think you'll be fine - Bring seasick pills
Bring Gravol - Take a gravol when you first get on the ship, before you go to sleep that first night, and when you wake up the next morning. Regardless of whether you feel sick yet.
Get scopalamine patches by prescription. One bit of advice though: Get a multi-pack. Take the time to test one before travelling for the cruise. Some folks develop vision problem side effects. I did, and my vision returned to normal shortly after removing the patch.
Seabands also work well for some.
Bring ginger candy
Generic forms of Dramamine and Bonine are available online cheaply. If you think your crew will be taking them every day of the cruise you will not only save money but probably make new friends by offering your extras to the numerous SeaMonkey(Δ)s who post in search of relief. Chewable versions may contain artificial sweeteners including aspartame, so people sensitive them should read labels carefully.
One of the ways that I avoid/lessen seasickness is to do my own rocking. When I am standing or sitting, I just rock (it does not have to be much) but it absorbs some of the movement of the ship and my inner ear is not so distressed.