I have to disagree. Though the listed items for the most part deal with things that are sourced from external stimuli, the act of cogitating on them for a while does NOT have to be external. Once you've read a piece of poetry or literature, heard a song or held a political discussion, you can go back and reflect on that. Distracting oneself with Angry Birds (the apparent favourite from reading so far) can prevent reflection on past experience or taking the time to extract meaning or insight from previous stimuli.
That being the case, I'm guilty of hovering over my OpenSudoku while stuck at the DMV, so what do I know?