The classic three lens rangefinder camera outfit of the golden age of rangefinder photography (1930's to 1950's) used by most aficionados of those times usually comprised a 35mm rangefinder camera body, a wide angle lens, a standard lens and a moderate telephoto (portrait) lens.
Famous makers such as Leica, Leitz, Contax, Zeiss, Nikon, Voigtlander and Canon spring naturally to mind with lens length such as 21mm, 25mm, 28mm, 35mm, 50mm, 85, 90mm, 105mm and 135mm being not uncommon. Typically a set comprising 28mm, 50mm and 90mm or maybe 21mm, 35mm and 85mm would not be uncommon.
For myself these days still being a staunch film user and devotee of the good old Contax G system, my my troika of lenses along with a G camera body would be the following:
Contax G2 (Black)
Zeiss Biogon 21mm f2.8 + Finder (Black)
Zeiss Planar 35mm f2 (Black)
Zeiss 90mm f2.8 (Black).
So although I have a set of six focal length prime lenses for my two Contax G2 bodies my most fluently used lenses of theses six, my three lens troika if you like, do indeed reflect a three lens outfit commonly in use back in the golden age of rangefinder photography - nothing really ever changes does it?
Indeed, given the one lens choice, I will often end up in the same place as those good old timers of yesteryear carrying just a 35mm lens, this being my favourite focal length of all (as it was often that of theirs too) with most of my film photographs being made on just such a lens - a Zeiss Planar 35mm f2 in my own case.