Steve, Personnaly I keep any Over-The-Counter remedies I can find aboard, as sometimes guests prefer a particular way, if they know what works for them. And they always forget to bring their meds. I also keep ginger snaps, and ginger ale aboard, and this can settle a quezzy stomach post-haste! And unless you have dietary restrictions, alot of salt helps. Saltine crackers can be great, even after the effects are past onset I have found.
Gee, I am really glad the 1st mate and I, have never been green around the gills before! It looks horrible, and I have ended trips before because guests have insisted, the fun was over for them!

But 1st I have them try the tricks mentioned above, it saved me more than once from having to return to port!
West Marine has patches, and scop is one brand that I have aboard, and it has worked in at least one case when the afflicted person needed it. Unfortunately sometimes nothing works, and this can be simply the person is prone to it. Some people who have ear problems where their inner canal was affected and equllibrium unbalanced. I find this especially so when as a child the parents had ear canals altered medically because of childhood earaches. As a Divemaster, I had many a student that when I asked them if they had a proceedure done as a child, more cases then not, they said they had motion sickness episodes too! Most were unable to complete SCUBA training because of this!