Don't think of how "useful" you are to people you love and who love you. That's the mindset of my own father - and he's an abusive racist, borderline fascist. He sees everything in terms of utility and has never had a relationship he didn't view as a transaction. Don't take that tack - it's toxic af and destroys relationships.

Just be there in the moment with him, and try to enjoy life with him. Unless your dad is like mine, he will appreciate that more than any notion of how "useful" you are.

Edit: think of something you both enjoyed doing in the past. Maybe some cherished memory you can recreate, or make something special for him. Even if you suck at whatever it is, he will recognize the effort and appreciate it