Enter the empty glass spice jar with kidney beans inside.
It works great. Of course, it will have to be discontinued when Cubby is big enough to possibly get the top off, because I think kidney beans are the very definition of "choking hazard."
But for now? Cubby is quite happy with his woodchuck rattle. And if Cubby's happy, so are we.
* Thanks, Aunt Marilyn! Anything that keeps Cubby quiet for 30 seconds is aces.