A derogatory term for a book or other printed material

I am looking for a contemptuous or belittling word or phrase that would describe something that has been published (not necessarily a book) but is of inferior quality, and a waste of paper. It can be a slang/informal term.

Specifically, I'm NOT looking for a term for a cheap novel (like 'pulp fiction' or 'airport literature') - there's plenty of expressions both here and in wikipedia, but the book I wanted to refer to does not have any plot. It's actually an activity book, if this information happens to be of any use. I just wanted to write something like:

This book turned out to be an unremarkable/uninspiring/etc. <...>.

I haven't managed to find anything satisfactory so far. I could probably just use something generic like 'piece of crap', but I was wondering if there was any more specific, paper-related term.

Consider "birdcage liner". Typically used in reference to newspapers, but widely understood as printed material fit only for a bird to poop on.

As a well-read AE native speaker, I've never heard of "pap", so I can't recommend it for a general audience. I like "birdcage liner" - quite evocative - but honestly, the most direct expression is the one you said yourself:

This book turned out to be an unimaginative waste of paper.

That will be well understood and is fairly common. Other expressions include not worth the paper it's printed on - quite common, but doesn't slot neatly into your sentence. For a single word, drivel is probably your best bet - it's both harsh and fairly formal in register, so more likely to be seen in writing than garbage or trash, which are probably more common in speech. Drivel also has the advantage of usually being used to describe written works, though it doesn't strictly have to, whereas garbage is obviously much more general.

While not specifically targeting written communication, drivel

drivel - silly nonsense. "don't talk such drivel!" synonyms: nonsense, twaddle, claptrap, balderdash, gibberish, rubbish, mumbo jumbo, garbage; informalpoppycock, piffle, tripe, bull, hogwash, baloney, codswallop, flapdoodle, jive, guff, bushwa; informal:,tommyrot, bunkum; vulgar: slangcrapola, verbal diarrhea "he was talking complete drivel"

Hotlicks said rag in comments, and I think that's a good one.

It has a meaning literally as "a bad newspaper", so it is derogatory, and wonderful as a close metaphor for other poor quality written works.

This book turned out to be an unremarkable, uninspiring, unedifying rag.