Ice melt and rock salt are mineral and do not go bad or expire. They are hygroscopic. This means that all moisture, even from the air, might melt, dilute or contaminate both ice melt and rock salt. Some products can be stored in the air-tight, resealable package they were sold in. If you buy a product offseason, don't open it until you need it. If you have product left over from last year, then you might want to invest in a salt storage box.