A long time ago in a law firm far, far away, I was a Litigation Paralegal. Many of my fellow paralegals would talk about how busy they were. They would eat lunch at their desk and always have some papers with them. They may have been creating a deposition abstract or proof-reading an index of a document production. They would work on these on their Metra train rides home.
This was in the early 90s, back before the days of connecting remotely to the office and working from home meant bringing a bunch of hard copy documents home with you.
I've never been good at looking busy. Either I have something to do or I'm looking for the next task. Often when I finish something, I submit to my Adult ADD and surf the web or find some other activity to stimulate my brain.
It's one thing to work through lunch in order to leave work early. It's another thing to consistently work through lunch in order to just leave on time. That is a sign that its time to look for another gig. Working some extra hours during a busy season is one thing. Having a busy season that lasts all fiscal year is another.