We all have one.
It might be a drawer, or a hall closet, or a garage. But somewhere in life, we have a pile of “random stuff” we might need. And every once in awhile, we actually go back to that location, and get the “whatchamacallit” we need to fix the “whosits” over there.
Your publications are no different.
Sure, you certainly want to keep graphics in a separate file…but what about that paragraph of information you plug in to your document 15 times a year? What about that neat logo you designed using shapes? And that piece of simple-but-really-nice clip art you spent 4 hours looking for–you don’t want to lose that, do you? Well…of course not–and most programs allow you to keep such pieces in a scratch area outside the image of the page… 
This is something you may not wish to do to your regular publication or publication template, however. Just like a real life drawer, every digital piece you add to a file makes it heavier (more kb or mb) and thus slower.
It would be far better to keep the clutter in one place. Just name a blank publication “Junkdrawer”, and copy things to it that you would like to save for the future. Every time the file (junkdrawer) gets slow and cumbersome (2-10mb depending on your computers speed) just create a new “Junkdrawer” File. Anytime you need the images/copy/borders/ideas, just open your junkdrawer, and copy in whatever you need.
Your document file stays clean, your copy runs fast, and all the “junk-you-might-need-someday” is tucked away for future use.

Thank you so much for the “junk drawer” idea! I am so guilty of saving things on the blank space in my publication. This will really help me in my quest to become more organized!