If you want to make music on the move, then buying a tablet for music production could be the best way to go. There are many options, at just as many price points, so there should be something for you no matter what your budget. Most tablets for music production can run the best music applications out there, including complete sequencers to arrange music, synths and other instruments like guitar and piano emulations. They are also powerful enough to handle software from some of the biggest names in the music production business, including Korg, Steinberg, Arturia, IK Multimedia, Moog and FabFilter.
Tablets use touchscreen interfaces, so you can drag, drop and create sounds with the touch and swipe of a finger. They also offer much more screen real estate compared to your phone, so make the whole music creation experience that much more fun and intuitive.