The method I used was great for organization but a little cumbersome from a mobility standpoint. Initially I planned on using a suitcase, but I found that my reference material didn't fit well in the suitcases I had and I wasn't able to organize things very well. So the day before the exam I decided this really wasn't what I wanted to do. I went out to the grocery store, pulled around back and asked some of the guys that were there if I could have some of their milk crates. The guy there said "Sure, grab some of those over there" and pointed to a huge stack of crates over near their dumpsters. I picked up three. After getting them home and cleaned up I noticed that they have warning labels on them saying that it is illegal to use them by anyone but the milk company and for anything but transferring milk. So I hope nobody from a law enforcement agency is reading this. In my defense I was given permission and they were being thrown away...
...anyway, back to my point. I used two of the milk crates to put my references in. I found them to be the perfect size to put my references in and I situated my materials so the spine of the book/folder was pointing up so I could read it and retrieve it quickly and easily and slide it back in place easily when I was finished. This method worked well in the testing facility since we were told that we had to keep our materials under our tables to keep the walkways open for the proctors.
The drawback to this method was that I didn't use a hand truck or cart with my milk crates. So to move them I had to stack one on the other, pick them up and just hoof it to the testing room. Two milk crates full of books is a heavy load, so if you aren't looking to get a good work out the morning of your exam I advise choosing an alternate or modified means of transporting your references.
Edit:
I still haven't taken most of my references out of those two milk crates which are still sitting in my basement (study room). The third one? Well it's been a great step/work seat that I keep in my garage.