Thinking of recycling, I made a sketchbook of old envelopes that were arriving regularly to my workplace. One side is perfect for markers, and as a bonus feature you have the address, registered and other post office stickers. The inside of the envelope is great for charcoal and pastell.
The hard cover is made of the backsheet of used drawing pads following the recycling line.
In between the pages I put silk paper to protect the opposite pages from charcoal – whatever fixing I use, charcoal always makes a mess. It did not make the binding easy though… But the result worthed the effort.