Plenty to do: make to do lists, write drafts to personal letters / complaint letters / business letters, plan life strategy, think of projects (like re-doing the lawn), doodle, sleep, read the airline magazine (airlines used to have a lot of other magazines), plan ff strategy, repack carry-on if hastily packed, clean up area around seat, pick at feet (no! this was a subject to a FT thread), listen to music, gather receipts and expenses, look out the window.

There are always things to do in an airplane. I've flown on one of the longest commercial flights and not become bored. I've flown on 2 hour flights and don't have enough time to do all of the above.