Best for slicing are THIN blades. That's why the best kitchen knives are so thin.
Of course, in a leisure folder you want some extra sturdiness as well.
With this in mind, the Military and Police are pretty acceptable slicers, but already relatively thick. From the other Spyderco models, I would rather go for Chokwe (a diabolical slicer with an acute tip), or Stretch 2. Possibly the Centofante 3 (less than 3mm thick blade) which is wonderful but the construction is maybe a bit light for camp use.
From the above, Chokwe and Military seem best suited to your usage because their open construction is easier to clean
Looking at other brands, Opinels slice extremely well (that thin blade again) and do consider the EXCELLENT Eka Swede 88, which has only a 3" thin blade but it is such a nice outdoor folder.