I don't recall a rubber ducky in particular although I may have had one. One thing I do remember was I had these little rubber frogmen. There was a small compartment at each frogman's feet. The compartment had a metal cap with a small hole in the middle of it. You put baking soda in the compartment, as I recall, pushed the cap into place, & it made the frogmen sort-of bob around under water while bubbles rose to the surface of the water in the tub. Or at least I think that's how they worked. It was a very long time ago...