You all will label me as a "geek"...but on the long flights I read my flight manuals. As far as I'm concerned it is pertinent and related to safety of the flight. Personally, I require a lot of recurrent study to stay sharp. Just counting company manuals I'm responsible for, not counting the AIM, etc...it numbers in the thousands of pages. I would just assume do it at work than at home.
FWIW, just staring out the window, un-engaged, is about as bad as reading or listening to music. Somehow, as a professional, you need to fight through fatigue and boredom andkeep yourself engaged and ahead of the flight.
I'm a big fan of doing things by the book. Stepping outside defined boundaries, in my experience, leads to bad things. A rigid flight deck is not desirable IMO. However, one that is too relaxed leads to complacency...and we know where that leads. I prefer a casual, yet businesslike flight deck.
Many times during your career you will probably be sneered at for doing your job in a professional manner. But, hey...I can live with that. It beats having your accumulated fortunes drained in a malfeasance and manslaughter lawsuit brought on by those you have harmed or potentially harmed.
In the present time in this industry, given the scope of attention it attracts, I think it's best to keep your actions in bounds.