You know, your bookshelf is full of old (or not-so-old) very expensive (at the time you bought them) programming books. Here’s a picture of a small shelf on my bookshelf…
In “Kindle’s times” now maybe you have an electronic copy of those books (an many other) on your favourite ebook reader / tablet.
What can you do with those books? Well, if you don’t have any particular reason to keep them and make them cover in dust, you can sell them on eBay or on a classified site (but you won’t get more than a few bucks for them) or donate them to the local public library.