Friendships.
I am lucky enough to work with some really awesome people. I am lucky enough to consider some of them friends. As I prepare to leave work, I realize that some of those friendships will follow me into my new job, that these people will stay with me and we will continue to be friends outside of work. It makes me realize how lucky I am to build relationships with amazing people and how happy it makes me to realize that people care about me in return.