In an ideal world, I'd work on one of the (excessively many) books or ebooks that I've queued up. In reality, I pick up my phone and refresh HN, play some Tetris, or maybe a training exercise on lichess.
These are the things I do every day and sometimes I feel like I'm a useless :(
I wish I had an answer for you. The closest I have is this: reading on a stationary recumbent bike at a gym seems to work decently for me, as long as the material isn't anything that requires serious focus, or taking notes.