I've been in more or less this situation in Charles de Gaulle on Air France. I was travelling with carry-on only and had bought a souvenir letter opener that I subsequently forgot about. I had arrived at the airport quite early and it was found at security and I was sent back.

I did in fact have a baggage allowance but I didn't want to check in my carry-on because it had reading material, snacks, music etc. The check-in counter declined to check in a single letter opener on the grounds that it was too small and would probably get lost or fall through a crack so I went to a newsagent and bought a roll of sticky tape (and a free plastic bag), one roll of tape and plastic bag later, I had something that could be checked in. It got a sticker stuck on it and rolled off down the conveyor belt, I collected it at the other end. It must have weighed about 500gm so if you are paying for baggage weight, it might not be very much.

I've been in more or less this situation in Charles de Gaulle on Air France. I was travelling with carry-on only and had bought a souvenir letter opener that I subsequently forgot about. I had arrived at the airport quite early and it was found at security and I was sent back.

I did in fact have a baggage allowance but I didn't want to check in my carry-on because it had reading material, snacks, music etc. The check-in counter declined to check in a single letter opener on the grounds that it was too small and would probably get lost or fall through a crack so I went to a newsagent and bought a roll of sticky tape (and a free plastic bag), one roll of tape and plastic bag later, I had something that could be checked in. It got a sticker stuck on it and rolled off down the conveyor belt, I collected it at the other end. It must have weighed about 500g so if you are paying for baggage weight, it might not be very much.