Mountain Lion Flash Drive

I have an iMac being shipped now. It comes with Mountain Lion.

When It comes, will the OS be pre-installed, or will it come with a flash drive, so I can install ML? I don't want to mistakenly wipe my hard drive or something of that sort, and not have something with the OS on it.

Or is their a way I can put the Mountain Lion Install on a flash drive, since I have plenty sitting around,

All responses are appreciated.