2x 40 min of train everyday. Best way to spend them?

I find when I commute that writing an email TODO list of the work I will be doing today, or a TODO list of things I want to do next on my side project. Generally it gives me lots of simple ideas.

A train trip can be disruptive. Take on tasks that are small in nature, and your thought process will not lose out on in-depth analysis of any one problem.