While monetary gratuities ARE absolutely appropriate and appreciated, when a Cast Member does something nice for you, it is really nice to show appreciation in a personal way - and some positions are not those that can receive monetary gratuities; Kids' Club & Lab CM's, the Cleaning & Maintenance Crew, Guest Services, etc.
Since the meals are provided, CM's onboard are charged "passenger" prices for their snacks. Things like chocolates, salty snacks, fruit candy, etc. are quite appreciated and really nice things to gift the CM's with; not 'instead of', but ABOVE AND BEYOND the monetary gratuities.
Our family usually brings an entire LARGE bag, FULL of individual bags of candy and salty snacks to liberally hand out to any CM's who we would like to acknowledge personally. We bring bags full to the Kids' Club to say, "Thank You" as well as to Guest Services. We have added bags full to the tips for our Spa Therapists. We also leave a line-up of treats on our bed for our Cabin Steward each day!!! It's fun to leave THEM treats since they work so hard to make our vacations so special! And they do appreciate it - and remember us for doing so! It really is so nice - and fun. Plus when the cruise is over, we have an empty bag for all of our FE gifts & souvenirs!!