Good Housekeeping's Heloise Household Helpline (hee!) has a unique use for a spare walnut:
Depending on the "color" of the wood, you can use the "meat" ‑- the actual flesh part of a nut ‑- to color over light scratches. Break a pecan or walnut in half and rub over the scratch several times. Then, rub with your finger till the area is warm, to help the wood absorb the oil from the nut. This usually works on light scratches.
Alternately, Heloise recommends using a crayon (or, uh, a table runner) on those darker wood or deeper scratches. Thanks, Marcy!
Pet Scratches on Wooden Furniture [Heloise Household Helpline]