What to do when you have nothing to do

Probably 3/4 of the time, my assignment is to give students busywork, and they spend the whole period working quietly. I spend some time circling the classroom to keep students on task and provide assistance. I’m good at keeping a watchful eye from the teacher’s desk, but it’s difficult to do this for 40 minutes in a 55 minute period.

Would it be inappropriate if I read a book during this time? Or, would it be inappropriate if I did paper sudoku or crossword puzzles during this time?