The second instrument I would recommend for a rhythm bag is an ocean drum.
There are several different styles of ocean drums, but I like this Remo model because the the children I work with like the size and multitude of colors. If you gently rock the instrument from side to side, the beads provide a mesmerizing and pleasing sound somewhat like ocean waves. It also can be tapped with a finger or hand or tapped on a knee. This instrument provides a pleasant auditory and tactile experience.
Some of the children I work with are overly mesmerized by the colors, motion and sounds and have difficulty attending to activities encouraging the use of the ocean drum, so with them I tend to use the ocean drum as a reinforcement or reward for completion of a separate task.