The sulfite family does a great job of clearing up MnO2 leftovers. I used to have a benzylic oxidation with KMnO4 that was my least favorite reaction in the world until I learned about that one.
Milkshake, the man the legend, had a post someplace on activating and storing MnO2 as an oxidizer. I'm getting ready for class but I'll look for it later.