Step 1: Rubber ducky's not the one
Pushed underwater to make bubbles, used as a boat, used to sink other boats, filled with cold water and emptied on some unfortunate sibling's head, squeezed to squirt water or simply used for good old fashion clobbering and splashing -- the fun is endless!
Plus, you never need to clean those nasty black mildew spots. Recycle, and replace it with a fresh one. Did I say one? Fill the tub!
Step 2: Construction
Step 3: Shovel and bucket
Step 4: Dress them up
Step 5: Bowling "lite"
10 (or 6) empty liter-sized plastic bottles
1 tennis ball
One hallway, preferably unencumbered with priceless, fragile artifacts
Patient and understanding downstairs neighbors
Take turns rolling the ball to knock over the "pins". Keeping score is optional. Game ends when neighbors bang their ceiling with a broomstick.
Step 6: Music
Using different types of beans isn't just to look pretty -- it affects your sound. For better musical control put lentils in one bottle, Fava beans in another, white beans in a third, maybe some rice or popcorn in the last one and start a band.