All the unframed pieces should be wrapped in cellophane/acetate. Usually when I do this I lay the piece facedown on a piece of cellphane, cut out around 2-3 inches larger than the artwork, then fold over and tape. This will leave you with an area of backingboard in the middle back. You can find D-rings or other kinds of hanging devices that you can then glue or double-side tape to the back of the piece. If it's going to be hung be sure to tape the cellophane on with a good sturdy type of tape, just so it doesn't somehow unstick.
Saying that, I've never heard of a show asking for unframed work to be prepared for hanging. But as long as the piece isn't too large it should be a problem.
I'd ask over in framing too.