Move all your iTunes music to it.
If I may suggest, two things:
Wiping the drive may be fine, and dandy, but you need to
repartition it as GUID, if you ever want to be able to boot from it, which is a wise precaution.
I also suggest a seven-pass zero-out, to clear all datum, and mark any bad sectors. (A zero-out can also revive some sectors marked as bad.)
After that, I suggest running disk verification, and then cloning your boot drive to it, so that if you boot drive ever develops a fault, that you may use it as a secondary.
You didn't specify the capacity, so asking for suggestions on what to do with it could prove meaningless. You could use it as a Netboot image device, a scratch volume for Adobe suite, a general datum volume, a save-point volume for torrent datum (never use your boot device for this), as a boot mirror, or countless other things. If the two volumes are identical in size, you can further make a RAID-1 set of them (this will wipe both).