Recycled, low-impact art supplies are hard to find, but many brand-name manufacturers have excellent environmental programs in place. Beware of cheap pencils made with unsustainably harvested tropical timbers - plantation timber is the best choice. Small pencil stumps might not be good for fine drawing - unless you have a pencil extender - but can be used for simple shading.
Derwent Cumberland have replaced nitro-cellulose solvent paint finishing with a UV cured coating, reducing energy consumption in the process. They also use leftover timber end cuts for some pencil manufacture. Their Graphic range come in Technical (hard, 9-H to B), Graphic (Medium, 4H to 6B), good for general and realist drawing, and Soft Sketch (H to 9B), sutable for general and expressive drawing. If you use a limited selection of pencils, choose your favorites from loose stock (which also reduces packaging).
Faber-Castell has a Brazilian reforesting project (certified by the Forest Stewardship Council), growing timber for pencils on formerly barren savannah. They also work to reduce energy consumption throughout product development. End-dipped color on these pencils reduces laquer use, and the natural wood case is pleasant to grip. Regular pastel sticks would reduce waste further, but if you prefer pencils, these are a good choice.
Cedar-Cased pencils from sustainable plantation timber, like these ones from The General's, are a good choice, especially if they are unlaquered or have a waterbased laquer (as used by Derwent and Faber-Castell).
Use up almost your whole pencil, adding balance and grip with a pencil extender like this one. More labor-intensive alternative is to lightly sand and glue the tops of two worn-down pencils together, making one double-pointed one.
Many artist like the consistent balance and solid weight of a refillable lead holder. Over time they'd probably be a good choice environmentally, as though made from metal and plastic, there is no timber or paint being shaved away, and the refills - at least in the case of the Sanford ones - seem to be minimally packaged. So a good choice if ou do a lot of drawing, provided you don't lose them!