I actually have a leather key case (Ghurka), and it fits in a flat pocket behind the keys. For years I did carry one, taped closed, on a split ring attached to a key ring. I currently have another in my wallet (in a folded, cut corner of a plastic bag, taped) that I have to remember to take out before I fly next time.

I wouldn't want to be without one. They weigh almost nothing, they're small and flat, and so long as you get real ones and not knockoffs, they work very well. I use them very, very rarely... but when you need one...

Case in point.. many years ago, I had agreed to feed the cat of a lady friend's sister while she was on vacation. The first day we had a huge blizzard, car travel was impossible, and I ended up walking (postholing through snow) for about 3 miles ("but I have promises to keep, and miles to go...").

When I got there the cat food was all laid out, but they'd taken the canopener with them on vacation. My choices were to use a $250 knife to open a can, search someone else's house for other possibilities and possibly ruin assorted implements not belonging to me, or posthole back a mile and a half or so to the nearest convenience store, buy a canopener, then back the same distance... until I remembered the P38. Problem solved, Tabby happy, I'm happy.

I have ALWAYS carried one backpacking. There's no other convenient way to open a can that's nearly as lightwieight, and it's so light it's worth having just on the odd chance you buy some canned food in a country store somewhere, or trade for some on the trail.

They also work fine as a striker for ferrocerium sparkers like the BSA Sparklite, so- throw the striker away, substitute a P38, gain in weight barely measurable with expensive scale, gain in utility huge. I keep a dozen or so spares in a drawer- they're cheap, so if one gets lost (or confiscated at a metal detector) someday, no big deal.