For me, it's not a particular knife (make & model) so much as it's a particular
pattern: the scout/camper/utility knife. I latched onto it after joining the Scouts 50+ years ago, and it always has been cutlery's home base for me.
Initially, it was an Imperial Boy Scout knife, of which the knife seen here replaced the long-lost original:
In more recent years, I've picked up a couple of the Ulster Scout model from that same era, along with various additional camper patterns, such as the Camillus MIL-K knife, Remington R-4, the Wenger Soldier, and the Vic Pioneer and Cadet.
However, for the past couple years I've settled on the Camillus Army Engineer's knife from WW2 (made 1942-44). I have three of them, two with the U.S.A. shield. That is what goes into my pocket every day now. (And it's accompanied by a Vic Classic, just because that's the
other most-core-like knife I own.)
(This photograph was taken the day I bought it. The photo doesn't show this, but the knife still has about 40% of the original mirror polish on the blades. I have also since cleaned it up soemwhat and pocket carry has also helped but the black staining is today pretty much as it shows here.)
From time to time, I'll carry knives in other patterns, but never without a feeling that I'm wandering away from home base. Ultimately, what always brings me back is the sheer versatility of the traditional 4-blade camper.