Congratulations on making your first game in Cocos2d. There are many possible extensions you could make:
The game currently only drops one drop at a time. It was set up to use an array for drops; however, you should be able to easily drop more than one drop at once.
Currently the drop falls behind the water bucket; this is not what the designer intended. Modify the game so the drop falls into the bucket, as shown in the following figure: