Prohibited item forgotten in hand luggage: what to do with it?

In the US, according to the TSA you have some options:

When prohibited items come through the checkpoint, passengers are given options:

1. Take the item to the ticket counter and check it in your baggage or a box provided by the airport.
2. Many airports have a US Postal Service or other shipping services area where boxes, stamps and envelopes can be bought so you can ship your items home.
3. If there is somebody seeing you off, you can hand the prohibited item to them.
4. If your car is parked outside, you can take the item to your car.

This option is probably not available everywhere (but it's available in terminals 2, 3, 4 and 5 at Heathrow), it only works if you'll be back to the same airport at some point, and the cost may be a tad high if you'll be away for while (but probably cheaper than the fees for an extra checked bag): just leave the item as left luggage!

The company managing this at Heathrow can also (supposedly) wrap, ship, deliver items, and they sell accessories.

Not sure how prevalent this is in other airports, but I'm pretty sure most major airport will have similar services.

Something like this happened to me some years ago. I was flying from Sydney, Australia to Bali, Indonesia with China Airways - I think!? There was a final hand-luggage check at the departure gate. I was "randomly" picked and my bag was checked. Unfortunately, I'd completely forgotten that my Leatherman Wave was in my hand luggage!

Apart from the initial shock of the security guard finding the above item, I was rather surprised that it hadn't been found earlier going through X-Ray. My hand luggage was basically my day bag that I'd been carrying around for weeks (I was backpacking).

Anyway, they were great about it. They gave me a "receipt" and the item travelled separately. I then picked it up from the "confiscated items" counter when I got to my destination. No additional cost, no time wasted. I think I was lucky!

I once realized I had my pocket knife with me and I was not checking any bags. I went outside and buried it in the dirt. A week later when I came back, I dug it back up.

Japan

The time I made this mistake with a multi-tool in Toyama (around 2007 I think), I simply (and even with my limited Japanese it was simple) brought the situation to the attention of the checkpoint workers, who handed me a plastic bag with a form on it to fill out, stuck the article in the completed form-bag, tore the receipt off the top and handed it to me, and made the tool disappear into the bowels of the airport.

After we landed at Haneda, I went down to baggage claim where I found the "forbidden articles" desk (conveniently labeled in Kanji, Romanji and English).

The only snag was that the man who was tasked with helping passengers get their bags off the carousel was also the person working the desk. So I had to wait until all the luggage was removed from the carousel before I could recover my tool. That last bit feels like a Japanese solution to me and I wouldn't be surprised to learn that it was done that way on purpose.

In San Francisco (and probably other airports?) there are small self-serve dropboxes, next to the line to go through security. You can take an envelope from the supply on top, fill it out, including writing your credit card number down, and they will ship the contents to you for about $20.

I did this a few years ago, when I forgot to leave my pocketknife at home. I felt like a chump paying the $20, but since the knife would cost me $30 to replace, I did it. About a week after I returned home, the package arrived.

My home airport has a kiosk near where the line forms for security that's meant for mailing things that can't fly. It's nowhere near as obvious as it should be, I wasn't aware of it until the day I found myself almost in front of it waiting for my wife in the restroom. I wouldn't be surprised to learn that the security people know about it and can direct travelers there but neither have I seen them direct anybody there. (I haven't seen them fail to, either--the only contraband I've seen caught was water.)

I would ask someone that is not going to fly to keep the item safe until my return, and offer money in order to do so.

Even though you are asking a favor to a random stranger, this is not as awkward as it sounds. And there are plenty of options you could choose. This would work better if the person in question lives in the same city as you, but it really depends on the circumstances.

In most of the Europe, if you are found with prohibited items you are given a chance to go back to the Airline counter and arrange a checked in service (maybe meaning that you'll have to buy a bag to put it in).

I have indeed seen counters that will pack and ship for you, at some expense. I believe I saw that in Zurich and London, but memory is foggy. I've also noticed long after that something prohibited went through without getting caught, which can be annoying in a difficult-to-describe way.

Going to post my answer from another question here again:

Same thing happened to me at Schiphol with a rather expensive Leatherman Tool. Went back out, down to the newspaper stand and brought a boatload of postage stamps. They were even kind enough to give me a free envelope (otherwise I was going to wrap it in a sheet of paper).

Dropped it in the mailbox and went back, took perhaps 15 minutes in all. Needless to say a very strange letter but was lying in the mailbox when I got back.

Some airlines (like Avianca in Colombia), have mail service that sends packages between airports, so another option could be sending the item to yourself and pick in your destination