I don't do that based on $$ earned, but on goal achieved. And I structured it a bit differently, to make it more interesting and fairer between me and my wife.
But to answer your question: Guitars. I always need one more guitar. And a new amp. Just one more amp. And did you see the new strings released last month? I have to try them, you know... for science. And if I bought a new amp, I have to buy another mic, you know?