I buy all of my Star Wars books. I get good hard copies of them and keep them in good shape. I checked out Lost Stars out of the library, and it was a huge mistake because a few months later, I wanted to read it again, so I bought it. I read it every May 4 now, so I'm about due, although I'm itching to pick it up again, so it may be April this year. I like having my other Star Wars books on hand as well, especially since they help fill in some of the gaps in between the movies. Force Awakens made so much more sense after reading Bloodline.
Other than that, if there are books I particularly enjoyed, I buy them. I have the Hunger Games trilogy (another series I'm kind of itching to reread), some Nicholas Sparks books, Anne of Green Gables, and a few others. There's another series I recently read that I definitely want copies of because they were SO good.