Many years ago, I had a friend called Shaun Ward, who was a mean bassist. When he didn't have a bass in his hands, I never saw him without a set of car keys with a leather key fob. He'd hold the keys in his right hand, and rotate his arm & slap his thumb against the key fob as fast as he could.
I've collected a lot of finger exercises for guitar that I can do while I'm at work, but can anyone suggest any for bass? Either right/left hand/finger strength, slapping accuracy/speed, or anything else.