Are the dead cells you're carrying around like your hair "you?" What about food? At what point exactly in the digestion process does it cease to be something

Are the dead cells you're carrying around like your hair "you?" What about food? At what point exactly in the digestion process does it cease to be something else and become part of "you?" Is your urine and fecal matter that's still within your body "you?" How about the oxygen in your blood? Is that you? Saliva? How about tears? When to tears stop being you and become something else?