1. A complete new harddisk
I bought a new harddisk and install window 7 on it and copy all my private keys in there, i don't bother to leave this harddisk in the pc, after the copy is completed i remove the harddisk and keep it.
While the other methods are OK, I don't agree with this. Imho a new HDD is already a purchase and the price difference to some 60-70$ of a hardware wallet doesn't justify the hassle. (
You know that magnetic disks need a refresh every couple of years, right?)
If one goes for cheap methods, paper is the easiest to store and hide. And if one, instead of saving there a private key, will save the seed of a wallet, most people will not even know what strange haiku he has there.