Depending on the meeting, just turn your camera off and turn up the volume. Wash dishes, clean home, eat a sandwich… If you cannot turn off the camera, then just work.

I’m assuming you want to do something productive because the meeting itself is not. Otherwise, doing something productive with your hands while being on a productive meeting will lead to you being not focused for the meeting… so what’s the point.

Can you be entirely nude below the waist? I'm serious. It would open up so many options.

Some people find it helpful to fidget with something in their hands during Zoom meetings, like a pen or a small toy. This can help to keep you focused and engaged in the discussion. Other ideas include doodling or taking notes.

If you have a lot of meetings, you may want to invest in a small whiteboard that you can use to jot down ideas or doodlings. This can be a great way to stay productive and engaged during long meetings.

If you tend to get fidgety during meetings, you may also want to try sitting on a stability ball or using a standing desk. This can help to keep your body active and engaged, which can help you to focus and pay attention.

something I can do with my hands

You really teed it up there.

A friend of mine discovered lockpicking helped him to stay awake during university lectures.

Not productive but you can play games on a portable game console, use a tablet, ...

Jeff Toobin might have a few ideas.