I don't carry a p-38 any more. Used to be everything came in cans. Rations were C-rations and while you could open one with a knife point a P-38 was just so very quick and efficient that not carrying one didn't make sense.

I never carried one on a keyring. Keyrings,IMHO, need to be kept as compact and light as practical if you expect to have to roll around on the ground. A big cluster of keys wears out pants pockets and leaves a bruise, or worse, if you fall on it. The fold-out blade on a P-38 is only about half and inch but driven into the flesh, ground in, and ripped sideways it can be quite painful.

I used to carry my P-38 on a string around my neck. A simple half-hitch in the string holds the blade in the folded position.

Now there aren't many things that come in cans and my Leatherman has an effective can opener. As much as I admire the simple efficiency and utility of the P-38 I suspect that my P-38 will mostly remain hung on my wall. I just don't see it making it out into the field.