This is my mini design wall that I have used for the past few years. It is a 12" X 12" piece of cardboard (off the back of a pad of scrapbook paper) covered with a piece of white flannel. This way, I can be mobile with the current projects I am working on. For instance, I needed some contrasting fabric to go with the commissioned project I a currently working on, so I was able to take this board to the fabric shop, and have all the other pieces there for comparison.
Now, we all know that while fabric will "stick" to flannel, but to actually transport it around to and from a store, I use a plastic folder (also from the scrapbooking craft). This plastic sleeve is perfect for taking my swatches into the store and use it to get the additional items I am looking to get in order to complete my projects.