From Earl Proulx's Yankee Home Hints:
* To restore stale/soggy crackers or cereal, place them on a cookie sheet and heat them for a few minutes in an oven at 350 degrees Fahrenheit.
* To soften sugar (or to prevent it from hardening in the first place), store it in an airtight container with a piece of grapefruit, orange or lemon rind. The sugar won't absorb the citrus taste. Replace the rind with another piece when it dries out. Alternatively, you can use a slice of fresh apple, which I've done in the past. It works especially well with brown sugar.