What's the meaning of "while I'm at it"?
The speaker's partner asks him to get a piece of cake because he is hungry. The speaker agrees and answers that he will get one for himself while he's at it. "While I'm/you're at it" is an expression used to tell someone to do something while they are already doing something else (such as a related activity). Since he is already going to get a piece of cake for someone, he might as well get one for himself "while he's at it," or while he is already doing it/going there. Ex: Can you get me some coffee? And a spoon too while you're at it. Ex: I'm going to the mall to buy something. Do you have anything you want while I'm at it?