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I second the post above.

Get an external enclosure (USB3 is best).

If you use either CarbonCopyCloner or SuperDuper, you can create a BOOTABLE backup clone of the internal drive, that will always be available as a backup booter if you get into an "I can't boot!" moment...
 
Get a Superdrive caddy and pop it in there instead of the superdrive if you don't use it
 
As I've heard, it's not data unless it's in at least two places. I installed an SSD in my older MBP and am using the old drive for Time Machine backups. I also have four external drives paired for RAW files, edited images and documents for my freelance business. Drives can die at the worst possible time and I want two of each just in case.
 
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