Question: Besides leaving the presence of the Lord and living in the land of Nod, what was Cain's punishment for killing Abel?
Answer: Abel was a keeper of flocks, and Cain was a tiller of the soil. As part of the punishment for killing Abel, the soil would no longer produce for Cain. Although Cain may have preferred death, the Lord placed a mark on Cain such that at his sight, no one would kill him. He was to become a restless wanderer living with the guilt of having killed his brother.
See Genesis Chapter 4.