... And some of the more prepared/paranoid stockpilers (ie: at B&B) keep their stash in airtight/watertight ammo cans. But, that's probably in case the house blows up or something.
To expand on some of the answers here, as long as they are kept away from dampness modern stainless blades will last indefinitely, even old carbons will last a surprisingly long time. I recently purchased 1,200 Gillette Super Blue Blades from the 60's still in the factory storage container. Because they had never been packaged for retail, they were coated in oil for storage. They were still like brand new blades even though the container they were stored in was not airtight and was covered in dust, even rust in a few spots.
