This is such a great idea! Instead of buying decor for your home and hoping it matches, you can erase all uncertainty by having your paint colors with you! This saves you the time (and gas money) of running back and forth to the store to return unwanted items.
There is a tutorial on how to put this together at Natty By Design. In the original project, she uses paint stirring sticks. If you carry a small purse, it might be a good idea to use popsicle sticks. I would suggest making multiple sets of these (one for your car and an additional set for a second purse that you carry).
***Make sure to write the room on the back of the paint or popsicle stick.