I don't know what to do when I have nothing to do at work

A little context: I work at a school as a building aide. My job is either super busy or super slow. In the moments where it's slow sometimes I manage to go chat with coworkers, other times I'm at my desk not really knowing what to do. I have an office but it's super open. Kids or teachers are always in and out of here grabbing or making copies. They're able to see what I'm doing on my phone and believe me, they look. Everyone here is nosy. 🤣 So I feel like watching a tv show or twitch is out of the question unless I just listen to it. I've thought about starting a hobby, I try reading but it puts me to sleep. ny suggestions?