I have carried a Coghlin's P-51 copy for 15 or 20 years in my wallet, up until tonight I thought it was a P-38 (Thanks for the informative link, KenK).

Whenever I use it in public someone always says how neat it is, so I give it to them and just replace it (they are inexpensive).
One winter day I was in a coffee shop (I think it was Tim Hortons) buying a hot chocolate for my wife, the machine ran out of chocolate concentrate and the young clerk could not find the opener for the large can. P-51 to the rescue, I opened the can then gave the tool to the clerk, she had never seen one before and really appreciated the useful little gift.

Mike