Love it when people leave books/magazines. I sometimes leave them when done as well for the next pax to enjoy. Whoever left me the 'Jack Reacher', thank you.
As for amenity kits, I don't see anything wrong with it. The main objection to the blanket thread was that a pax grabbed it BEFORE the flight, not after. If someone reached in and ninja'd my amenity kit before takeoff, I would certainly object.
If unused, I leave it in the wrapper and put it back where it was when I boarded, hoping they reuse them and don't throw them out.