I’m going to cheat and say my existence.
Just the very fact that I am alive. Because that in turn gives me the opportunity to be grateful for my friends and family, my skills, good luck and opportunity. It means I get to look at the world, and the universe, and find it beautiful. My good luck means I get to wake up, go to a tap in my house and drink a glass of safe water. My opportunities, history and drive allow me to rent a space to live in, to work for myself doing something I enjoy and give me plenty of interesting experiences to cherish and remember.
I am grateful for all of these things, and many more, but I couldn’t be if I didn’t exist in the first place.
Or cheese. Cheese would be my second answer.