We've previously explored the brown-sugar-loosening powers of a slice of bread, but if you want to keep your dark brown stuff from clumping, grab a couple of marshmallows.
My own household has cabinets that tend to dry the heck out of anything, and would-be bakers spend a good amount of time cursing our brown sugar. This little food saver seems to make sense, given marshmallows' ability to hold moisture in nearly any conditions. And it will save us from having to sacrifice bread to make cookies, which always seemed like a strange Faustian bargain.
Brown sugar fix [Chicago Tribune]