My last job they really didn't like us doing nothing during down time, they really wanted us to be sweeping the floor or some other busy-work. There was a lot of work to be done like that, so it got boring, fast.
Now I have a job with tons of downtime and my boss is explicitly fine with us reading books, playing video games, watching Netflix, etc. as long as we are responsive when customers come in. It's a great gig (although low-paying), especially for a college student.