I don't have to, but I want to. [ not for any noble - or nerdy - reason. But it's because Kaneki wants to show the government there is nothing for them to worry about. Wants to show them he is a good citizen and is still working even if not being paid - or not really needing it. In fact, Kaneki has no plans to work for much longer.

He takes a sip of his coffee - the flavor is good enough for an American coffee and at least they didn't burn it when making it - and nods softly after ]

I know. If I'm in a pinch, I will let you know. [ he already expected the offer ]

... it's mutual, you know? If you need anything. [ he isn't talking about money. ]