I have a few of the excellent 
Ritter RSK Mk5 knives.  I think it's one of the best choices for super-minimal PSKs.  Sure, a big fullsized fixed blade is optimal but I feel the Mk5 provides exceptional functionality for times when size and weight are big issues.  I really like the Mk5 for splitting small sticks into very small kindling, which feels sketchy with a Spyderco Ladybug or small Swiss Army knife.
I don't do neck knives.  If I'm using the Mk5 then I have pulled it from a small PSK and I have found that the little thing is easy to misplace, as is the sheath.  It's not going to be riding on my belt or in neck knife mode.  I like to put my hand through the included lanyard so that I can't drop or lose the knife.  But how to retain that little sheath?  I have learned the hard way that if you set something down in the field unsecured, it is easy to lose it.
So I'm trying out a couple of tweaks.
- I made a little keeper leash for the sheath from   
GloWire dyneema cord. This lets me keep the sheath secured at my wrist and makes re-sheathing quick and easy when I do a different task but am going back to using the knife soon.  Can't lose the sheath this way.
- I slapped on a patch of dayglo orange duct tape on either side of the sheath for better visibility if dropped from the kit.  And the GloWire has a retroreflective stripe so if I drop it at night, a quick scan with any flashlight makes it show up well.
Not rocket surgery, just some useful tweaks.
 
  