Consider writing a simple Android or iOS app, such as Tetris, from scratch. This should not take very long and has intrinsic rewards built in, like seeing your progress on your phone and showing it off to your friends or prospective employers. You can also work on it during the small chunks of time available, since a project like that can be easily partitioned. Figure out which parts of getting it from the spec to publishing on the Play/App store you like and which you hate. Record your experiences and share them here once done.