Free code camp. It's trivial (non distracting effort), but even then taught me some nice skills like web accessibility and how to use array.map()

Codepen and Dribbble are nice too, just browse around looking at art and look like you're working. It beats news sites in that you can discover a new, useful thing.

Also you can meditate. Maintain concentration for 2 mins straight. It's not hard, and helps you regain composure.