Tricky question - Coz as like most of us it varies.
If you'd asked me a year or so ago (before I joined MTo) the answer would have been very easy - Four
My Huntsman - So standard toolset plus wood saw and scissors - scissors are pretty much a must have for me
However these days, typically I carry a Vic Climber or Wenger Traveller
during the week (office job)
And often the 5 layer Woodsman (= Huntsman + Explorer Ph/Mag glass layer) at the weekend.
I also own a Ranger (= Huntsman + Metal file)- But find I much prefer the Woodsman
I nearly always have a Classic in my pocket or on a keychain too!!
So I voted three - As a kind of average / most days of the week answer