What we have here is the Behrens board used by Chunk, washboardiste of Gutter Puddle from up in Vancouver, BC. He describes his add-ons as follows:

I added 3 measuring cups all different sizes
The one mounted on the bottom makes a higher pitch splash sound
The one above the bell makes a deeper tone splash and the small one mounted on the side makes a high “pop” sound
My cowbell is also in the tone of g

Gutter Puddle is a really interesting trio with a washboard player, an accordionist, and a lead vocalist who also plays guitar, uke, and mandolin (and maybe more, for all I know).

Check out their version of “Saint James Infirmary” here. Highly recommended!