Put them in a fireproof vault and bury them in a reinforced cement tomb in the back yard. Barbed wire, guard dogs and alarm systems with 24-hour guards also work well.
Seriously though, as a person who has helped many a body who has lost their original discs, it takes far more time to do a system repair/restore than if they were available. One thing that I do for anyone who has a new out-of-the-box system is take the documentation and discs and put them all into a legal-sized clasp envelope and use double-sided tape to sick it to the side of the machine, or to the underside of one of the walls of their desk. That way they don’t get lost in a drawer or box “somewhere.”
I know it sounds cruel, but I also have been charging for replacements for discs lately, mainly because it’s a major PITA to gather all of the stuff necessary to get a system running again. If you have your restore discs, you get a discount though! So it evens out.
And I don’t care who told you that it’s illegal, I am telling you MAKE COPIES! It’s not illegal unless you put it on multiple systems or a system that it’s not licensed for. That way if the originals get lost, TA DAH! You have backups.