restore/install disc

How can I make a restore/install disc for my new retina 15" MPB?

You can put Mountain Lion on a USB stick and have for safe keeping, and if you follow the instructions here you should be fine.

How to Make a Bootable OS X 10.8 Mountain Lion USB Install Drive

But the easiest way is with Lion Disk Maker and download it and read up about it here.
I would personally go with the Lion Disk Maker way

HTH

Cheers

A related question from another 'new' OS X user - my r-MBP is being backed up w/ Time Machine - I've also made a USB drive w/ the Apple 'Recovery Disk Assistant' - quoted information below from the link - I'm just curious what the advantages and/or disadvantages apply to this means of disk failure recovery vs. the two methods mentioned in the previous post? Just wanting to know if I've done enough or whether I should also add another layer of protection? Thanks all - Dave

Open Recovery Disk Assistant and follow the on screen instructions to create a Recovery HD on the external drive.

When the Recovery Disk Assistant completes, the new partition will not be visible in the Finder or Disk Utility. To access the external Recovery HD, connect the drive, then restart the computer and hold the Option key. Select Recovery HD from the Startup Manager.

Click to expand...

The USB thumb drive, which is bootable when installed using Lion DiskMaker, is a great way of formatting, partitioning and installing the operating system in the event you have a disastrous hard drive failure. And it is free if you have downloaded from the App Store.