Apple Slices Help Keep Brown Sugar
I found out a great way to keep your brown sugar from going bad and hardening up into a rock: seal in an apple slice. I imagine this would work with any moisture-retaining object such as a fresh slice of bread or a ceramic object of some kind that had been soaked in water (see: Brown Sugar Bears). But not only does the apple slice keep the brown sugar moist, it restores previously semifossilized brown sugar to its former pliable glory.
Seriously, we had some brown sugar here that must have been hard and dry for at last 6 months.