Are you allowed to read a book unrelated to chess during a FIDE rated classical tournament game? I myself have done this a few times whilst studying for exams, but was never sure if it was allowed or not. I am 2100 so no one ever mentioned it. I'm hoping someone can post a definite answer.
There are two sections of the FIDE Laws of Chess which are relevant.
188.8.131.52 During a game, a player is forbidden to have any electronic device not specifically approved by the arbiter in the playing venue.
11.5 It is forbidden to distract or annoy the opponent in any manner whatsoever. This includes unreasonable claims, unreasonable offers of a draw or the introduction of a source of noise into the playing area
Use of a Kindle or other electronic book is governed by the first. You will have to get the arbiter's permission to read such a device during the game (or even to have it in the playing area) and this is unlikely.
For a traditional book printed on regular paper you just need to do it in such a way that it does not disturb your opponent (i.e. don't rustle the pages, put the book down noisily, etc.) as covered by 11.5. Although you would be well advised to talk to the arbiter first to clear the fact that the book contains no chess related material.
I have seen this done during FIDE rated league matches with no problems but not in large tournaments.
It should be okay but as the rules do not explicitly address this some picky opponent and retentive director might ban it because it might somehow give you an edge.
The closest thing which I could find in the FIDE Laws of Chess is
12.3 a. During play the players are forbidden to make use of any notes, sources of information or advice, or analyse on another chessboard
12.3 b. Without the permission of the arbiter a player is forbidden to have a mobile phone or other electronic means of communication in the playing venue, unless they are completely switched off. If any such device produces a sound, the player shall lose the game. The opponent shall win. However, if the opponent cannot win the game by any series of legal moves, his score shall be a draw.
Best would be to ask the TD before the match if you can read a non chess book.