Hitawci, that is partly a question for the supervising PI, but in Chemistry they could be doing literature reviews, or writing up results for a paper on work they've already done in the lab. I'm guessing that in some other departments remote work is even easier. I'm not sure what math grad students do, but I imagine they don't' have to be on campus to do it. Even many of our chemists are computational, and can do their work fully remotely, so woudl be able to do it from a hotel at a conference, in the evenings.