Books should always be celebrated, of course, but it is good to have a specific event which people can focus on and I love the idea of giving away books to get people into reading. I very much hope that people are now reading who might not otherwise have been.
Some of my earliest books were the classic collections of fairy tales. I don't know if there has ever been a survey done on this but I wouldn't be surprised if a significant proportion of people's most remembered books are the ones they read most in childhood. The great thing with books of course is the love of them could and should stay with you for life. They take you into other worlds. And if you write your own you get double the joy - the joy of inventing such worlds and then reading about them!
How many of the classic fairytales would have been lost had it not been for the Brothers Grimm, Charles Perrault and Hans Christen Andersen collecting the old stories, writing them down and then, even better, adding their own to the mix? That is how books live. We treasure the old ones, we write new ones and it all leads to a greater world of literature for us to enjoy.
Do characters in your fictional worlds write? What would they read? How does their literacy affect their lives (for good or ill)? How are books handled in your fictional setting? Are they treasured or feared (and as a result banned)? Who allows what books to be read and written? There are bound to be stories in answering those questions!