I once turned up on the airport with my carry-on luggage being a small daypack that contained two things:
1) A gallon of very high proof alcholol. (Let's just say there was a lot of Kalman filters that needed cleaning that semester).
2) A 5" Mora knife (the wood handled Mora Classic).


After X-ray, no one cared about the contents of my one gallon canister - but the knife was not allowed on board. Even pre-9/11 you were not allowed to carry a 5" fixed blade knife on board. The easiest solution suggested by the clerk was just to "tag" the bag and put it in the cargo with my checked in luggage. Which wasn't such a good idea, since the canister cap was not sealing properly. You don't get very popular spilling alcohol all over everyone else's luggage. I had to keep the can upright, which meant it must go with me as carry-on luggage. I suddenly realized that I did NOT want to explain in detail exactly WHY I had such a grudge against putting my daypack in the cargo hold. After all, highly flammable liquids are not that popular among airline crews...

The problem was solved by putting the Mora knife in a cardboard box labelled "extremely dangerous items - not carry on luggage". This did not hold up very well to the rigors of checked in luggage - at conveyer belt at the other airport, there was the sorry remains of a squashed cardboard box lying beside a Mora knife... It takes a bit more than overworked, underpaid luggage throwers to destroy a Mora.

In memory of better days, where you could find solution oriented airport security personnel...