Get an eBook.
My daughter who lives in NYC says their selection of e-books is fine. She knows someone living in California who pays $50 to be a member of the NY Public Library just so she can borrow e-books. She wondered if I would be interested. Maybe.
And check it for viruses. 
When I lived here before, there was a man who checked out a large number of the same books I did, prior to me reading them, and he would write comments in pencil on almost every page. The blank end pages would then have a several-paragraph commentary that always started out, “As a gay man…”
He started his essay this way no matter what the book was about.
I’d sure like to find one of those!
I’ve also found all kinds of things in used books, including credit card statements. Folks, if you’re going to use them as bookmarks (I plead guilty myself), REMOVE them before passing them on, whether to the library, Goodwill, a rummage sale, etc.
In my old town, we found photographs and other souvenirs in books. I got a poster board, stuck them on with scrapbook-quality adhesive, and wrote “DO YOU KNOW THESE PEOPLE/IS THIS YOURS?” on it. We did return one photograph to its rightful owner.
For the win.
I know. Those crushed dead trees are so… so… twentieth, don’t you think?
Concur. I used to work in a building that had a book drop that worked like a mail slot, and simply delivered books from a hole in the exterior wall to a bin on the inside of the building. They stopped using it sometime in the 70s because it had become a conduit for noxious items. It was replaced with the more modern style of external standalone book drop with a wheeled bin inside.
N.b.: neither of those images are from the library I worked at, nor are they meant to resemble exactly the book drops of that library; they’re just for illustration.
Does a reader of e-books use bit coins for bookmarks?
I think I have heard of bacon being found in library books, but I doubt if it is common. I believe that teh most common thing found left in library books (apart from just scraps of paper used as bookmarks) is money. I expect one dollar (or whatever) bills are lot more common than hundreds, but I recall once seeing on TV seeing a librarian counting out a big stack of bills as once found in a book.
“This book is crap!” 
It’s not just books. I’m astonished how dirty and scratched many library DVDs and audio CDs are.
Calibre free software handles most formats and is easy to read.
This cat was found in a book drop one winter morning, and two best-selling books have been written about him.
http://www.deweyreadmorebooks.com
My local library has several branches, and their book drops are attached to a conveyor belt with an electric eye that diverts the books and other materials into a box that will go to this or that branch. One branch even has a camera attached to it, so you can see your book go into that box. Children of all ages are fascinated by this.
Former librarian / library director checking in here. (hur hurr)
Yes, I’ve found both cooked and uncooked bacon used as bookmarks. (The uncooked bacon soaked the pages with grease; I’m pretty sure we had to get rid of the book). Also razor blades, feminine products (thankfully unused), lots of photographs, and documents of every description, including money, social security cards, credit cards, etc. It was quite common to receive books in the book-drop that had been dunked in both clean and unclean toilets (those were nearly always a dead loss, always in the case of ‘unclean’), spattered with snot or vomit, coffee spilt, you name it.
The vast majority of library workers/ libraries will not knowingly return a book to circulation that has been infected with something or smeared with something gross & uncleanable. That said, I did find a library book on the shelves yesternight with a Skittle crushed between two pages that could not be removed. That might have been in-library damage, though.
We had one patron at a library where I worked whose house was so infested with cockroaches and other vermin that they would come spilling out of any DVD or VHS he returned and also drop off him personally at times (though I didn’t see the droppage myself). He was politely asked by the director (not me at that library) to avoid library services until he could remove the insects from his person and refrain from returning materials brimming with them. Bless his heart, he had quite an eye-watering stench as well, though I had many library patrons over the years who did. He did clean up his act and return, though he still brought in cockroaches fairly regularly in his multimedia.
Oh, and the many, many library books returned with a stench (not just by him) were buried in clay-based kitty litter to remove it, at least at my local library.