Bring padded envelopes &/or stamps in your purse/backpack/other carry on equipped to hold that kind of stuff. That way if you find you have a pocket knife on you right before the flight, you can always mail the thing to yourself.

Chris had to do this once, and it was enough of a pain in the ass (yet totally worth it, it was this swiss army knife he's had since he was 14, so he didn't want to lose it) to remind him to pack the knife in the suitcase the night before ever since. =P