it's a great idea and probably could be another thing they could charge you for, even though it would result in fuel savings from the airline's standpoint.

I've also heard that if you need a new pocketknife, people that accidentally carried them up to the check-in and want to retrieve them when they come home will bury them in the sand of the ashtrays.But I've never checked this story.

People might pay to store a nice knife.

Do airports have rentable lockers? I know they have them at train and bus terminals. These would certainly work, though they might want to have some kind of security check to make sure nobody puts a bomb in one.