Everyone had a pocket knife when I was in school. And the teachers/principals didn't care much about it ... it was considered perfectly normal and non-threatening. But that was back in the 60's and 70's and things are quite different now. Now you get expelled for what was once considered normal behavior.

I wonder what they'd do these days about our "stink pens"? You take a metal ballpoint click pen. Remove the ink refill. Cram a strike-anywhere match up inside the top half, head facing downwards. Take a girl's bobby-pin and snip off one leg of it so it looks like a long skinny letter "J". Drop that into the bottom half of the pen so the "J" hook grabs the top of the spring inside and the end of the bobby-pin hangs out the end of the pen. Screw pen back together. To cause a stink, pull the bobby-pin end against the spring tension and release sharply. Discretely put the pen back into your pocket when done. It stinks worse with plastic pens, but they don't last as long as the metal ones. Especially fun with the substitute teachers who hadn't learned about these things yet!