Laptop + mouse + headphones works for me! I’ve recorded some albums on the train with this setup. Here’s one:
My non-computer-musician friend got lots of mileage out of his suitcase setup when we toured on the train a few years back. His rig from the back is the cover of this one:
^ That wasn’t recorded on the train, but we rehearsed our set on the train!
Edit: I wish I had a pic of the inside, but it seems like this is a fairly common thing now? He built eurorack rails and a power supply into the suitcase, and filled it with various modules – including a raspberry pi with a custom DAC that we used to network our rigs together…
Edit edit: oh here’s some pics! http://giganticgallery.info/tiny-concert-series/he-can-jog-and-dann-green
You can kinda see inside the suitcase in this one: