It isn't books per se, but education itself that is essential for society and individuals to survive and flourish. In Fahrenheit 451, books symbolize education, which leads ultimately to freedom of the mind. It was no coincidence that slave states in the United States criminalized the teaching of slaves to read. An educated mind is a free mind.
Forced ignorance is, in my opinion, the worst type of subjugation that can be inflicted by one human being on another. Government-enforced ignorance is tantamount to intellectual genocide.
Look at the reason for book burnings and you can find the reason why books are essential. Book burnings that have taken place in the past have been because the burners did not want people exposed to the thoughts and ideologies presented in the books. Even if one does not agree with an idea or ideology presented in a book, the words usually spur the reader to think about his or her own ideas and ideologies. Books present facts about history, showing the mistakes that have been made and the gains that have been made. If one is aware of what has not worked in the past and of what has worked, then one has a better idea of what to do in the present. Books give people that information. Books open the readers' eyes and minds. The books don't have to be just history and philosophy books either. Sometimes a story will have an idea presented by one of the characters that might get a reader thinking. Sometimes a poem will display an idea in such a way that a reader is moved by the words. All of this makes a person think and that's why books are essential. People who do not read only know what they are told. They do not know the whole story behind the 5 second soundbyte. Ignorant people are easily led to believe whatever the tellers want them to believe. If the media shows an overflowing river in rural Indiana on the evening news broadcast nationwide, then someone watching might think the entire state of Indiana is underwater. A reader might find out that it was only one river that overflowed its banks. A society will not survive as a free society unless the people in that society go past the evening news soundbytes. A picture may be worth 1,000 words but 1,000 words can explain the entire picture.
Books are essential not just for enjoyment, but are the backbone of the educational process in the form of textbooks. Not only would we lose our enjoyment for escapism and adventure if we didn't have a certain type of book, but without textbooks, advancing as an individual and as a society will take longer.