Upon starting training I inquired of the old rec.alt.aviation (I think that was it) usenet group as to what I should buy. One response was "Get a Sporty's catalog and order one of each." It did have a smiley with it...
That said, as a renter in a series of clubs, I carry a flight bag with 2 headsets (unless I know I'm going to have more passengers) charts (yes, I still carry paper sectionals) and assorted flashlights, pencils, portable etc. If I had my own plane, I'm sure a lot of that would stay in the plane.