Go stand in the yard and stretch your arms out to the sides. Now spin around. Slow or fast...it doesn't really matter. The space you are in is your "circle of influence". Notice I didn't say "control"? I lost my Mom. It was hard...Very hard. But like you said, "what can one do?". Go outside and spin around. It might make you feel better.
I'm sorry man. Try to enjoy your father as much as you can and reflect on the impact and time you've spent together. Just try to make him proud by living your life to the fullest.