I mainly use a smallish case with shoulder strap which was originally bought for an SLR camera.
While it's good to keep everything together and secure if travelling with it, the whole ethos of Mavic is compactness and portability - grab and go, carry it with you easily.
So you want more options. A lot of the time you only need the Mavic with the one battery in it and the controller 

Have this one too by Polar Pro which holds everything but charger - good option if three batteries might be needed, and incredibly compact compared to the Phantom small suitcase things.