You are responsible for your impact on everything, both around you and yourself. Gromit answered this perfectly:
You are accountable for the consequences of your actions. You follow through on what you say you are going to do. You own your shit. And you aren't a burden on others (within your capabilities, obviously).
And let me extend what it means to the rest of the questions:
Everyone & everything your personal agency touches upon, including yourself.
Which should also help you understand why this is the case:
It always seems connected to a social group, and it's always often about the more influential members of that group. It seems like socially agreed roles. But then, there's that line from Spiderman, "With great power, comes great responsibility", being a superhero is not a socially agreed role. What is it exactly?
The more influential you have, the further the reach of your own personal agency. The responsibility doesn't result from the group agreeing that it's there, it will be there even if nobody in the group knows about it - It's simply that in the case of social power, the group's agreement is what gives a person the influence to begin with. For contrast, Peter Parker's power doesn't come from any social role given by others, but they extend impact on others and thus his responsibility for others, even if the social agreement is not only lacking, but out right disputed (Many if not most of the city inhabitants view him as a dangerous outlaw).
Isn't that a relative thing? Isn't that dependent on what you personally care about?
There is a distinction to be made here:
You feel compelled to be responsible for what you care about.
You are responsible for your actions, regardless of what you care about.
I love shrimps, and in my love for shrimps I have helped finance the murder of dozens if not hundreds of shrimps. I don't really care about the well being of individual shrimps, which means I don't care that I have harmed them. But I am still responsible for harming them. If the shrimp families of the shrimps I've eaten had a trial and asked who's accountable for the murder of their fallen brethren, holding me, the fisherman and the cook responsible would be completely true, regardless of how I feel about it, regardless of whether I care. If I deny that responsibility, that doesn't mean I am not responsible, it means I am now owning up to a responsibility that's going to exist regardless of how I feel. Agency bestows responsibility, you are within your full right to choose what you care about, you do not get to choose what consequences of your actions you are responsible for.
Warning: Mind fuck territory ahead.