I would contemplate the profound solitude, reflect on humanity's legacy, and seek ways to document our existence. Loneliness would be my companion, but introspection, my solace..
As the last person on Earth, I would need to adapt to the challenges of being alone, both practically and emotionally. This might involve developing new routines and coping strategies.
I would despair but I would travel the world and do things I was never capable of, but I would probably feel very alone and it wouldn't be worth anything.