Then the question may also arise "what about the inside?" What about adhesive residue?
I am assuming that rather than bags used to pack and market scallops, these are the bags used by snorkelers to gather scallops and they themselves, decorated or not may not even fall under Food and Drug Administration rules but that your client is merely being cautious (or wanting an additional selling point) I believe that most are poly mesh, and I saw one clever "hands free" one that is like an apron pouch.
So, for these, an approved ink for what material?