Whatever works best for a one-man-band setup. Bass (or moderately sized) drum is 1st on the list isn't it? And if we're going for 3rd and beyond, symbols (on the knees) and kazoo would be next! Or harmonica if I wanted to be really sophisticated!
On a more serious note, I quite fancy the flute so I can impersonate Ian Anderson (although I can't stand on one foot for very long!). Or revisit the saxophone which I started to learn when I was a young teenager.
"Music washes away the dust of every day life." Art Blakey
"If I don’t practice for a day, I know it. If I don’t practice for two days, the critics know it. And if I don’t practice for three days, the public knows it." Louis Armstrong