At least one (usually 35 or 50).
Often two, with two bodies (35 and 75).
Sometimes two extras, ultra-wide (15-18-21) and long (90-135).
Depends on how long I'll be away for, and where I'm going. Ten days away in the Pyrenees, probably 5 at least. Out for the day, quite possibly 1 or 2.
But they don't weigh much or eat much, so I don't worry about the extra ones. All I care about is the time I waste changing 'em.
Cheers,
R.