What if your opponent was taking quite a while for moves, and you wanted to do something else with your brain. Would it be permissible to read a book for a few minutes? How would anyone know it wasn’t a book about chess? Would you have to show it to a TD?
I think it would be rude and disrespectful.
I knit during long meetings, and find my focus is better than if I’m not knitting. Thus, I’ve considered knitting while playing chess. Guess I’d have to work without a pattern, though.
Madam Defarge, I presume? 
Hmm, I wonder how long MCO would be as a scarf?
I agree with Smith that something like that is rude and disrespectful.
How about if you are reading not at the table, but off to the side a bit. Would the TD want assurance that it was not a book about Chess?
Or how about writing a letter while playing? That would take one’s mind off the game. “Hi Dear, wish you were here!” Postcards and such.
What?! 1. … c5?! Off with his head! 
Sorry, can’t afford that much yarn.
What if he were reading the Rulebook during the game?
I’ve seen it happen and never had a complaint.
I’m thankful that some kid who had to get a reading assignment done during the weekend has also chosen to play chess.
To answer the question “Would you have to show it to a TD?”, the answer is yes. If I saw a player attempting to read something while trying to hide it, I would demand to see it.
A player once asked if they could read a chess magazine after they had made their first move but were waiting for their opponent to show up.
You mean reading at the chessboard, or stepping away and reading a bit? At the chessboard would of course be more convenient, because you’d know the instant the decision was made on the other side. In a way it’s polite to read, because your mind will be fresher for the game then, rather than staling out on the game endlessly.
I don’t see how it could be considered polite. To me, it comes across as “you’re such an unworthy opponent that I can sit here and read this book and still beat you.”
Regarding a kid who is doing a reading assignment while playing chess, he’s probably not doing a very good job of either. He should skip the tournament and do his homework.
The best policy may be to invent limericks in the mind, to take a mental break. Alas, the humor may be hard to suppress!
My chessmate has now roared with laughter,
My poor state of mind is a-shatter.
With worries that pang,
I see a zugzwang, –
My game is entirely a-splatter!
Chess haiku might be easier to write, or at least shorter.
I have had opponents pull out a novel and read between moves. I think it’s highly rude. I think when an opponent is doing something totally unrelated to the game itself, that he’s not showing his opponent respect. I don’t care how much one out rates the opponent, show the player that you are taking the game seriously.
But I’m assuming that it’s okay to read a novel while you are sitting at the board, waiting for your opponent to show up.
Also, not exactly on topic but what are the rules about eating/drinking at the board?
“It is forbidden to distract or annoy the opponent in any manner whatsoever.” Interpreting this is a judgment call for the TD. You have to be careful with this, since some players read it as a blanket prohibition of any conduct they find annoying, which it isn’t. (“My opponent is staring at me! Make him stop!”) And not only among little kids. Remember the time Mecking asked the arbiter to tie Petrosian to his chair?
What if I have a laughing fit during a game? How can I help it? If something is funny, it’s funny! 
As a TD I once watched a GM read a book while playing a NM. I assumed the book was for a college class considering the title. The GM is pretty chill, so it wasn’t an insult (he had a different book the week afterwards). The NM won the game. The week after, the GM almost dropped a game to a B player, if the B player had better endgame instincts.
The moral? They chose a distraction to their own game; beat them. Taking offense only gets your blood pressure up and clouds your board vision.
It’s not necessarily rude. Some players just can’t seem to concentrate on a game more than a few seconds at a time (I’ve known a few). It’s probably less disruptive/distracting than the OTHER things they could be doing (and that I’ve seen in tournaments). I’ve known some people to play in two sections at the same time and rush back and forth between boards. Others bounce up after every single move and wander around restlessly. And then there’re the more objectionable things…
All in all, at least reading is usually quiet.
We once had a player have an epileptic fit during a game. It wasn’t his fault, but he still had to leave the playing room.