I am not sure I agree with this.
Part of the charm of Divnity is the that you never really know what is quest items and what isn't. This goes well in hand with free nature of the game. You walk around and experience the world how you like it.
That said I do agree that it is maybe too easy to mess up the game. Maybe it should be possible to right click items and mark them as "important". Items marked as important can then not be sold or dropped or carried by henchmen.
Still that's highly un-user-friendly. As you always pick-up quest related items; especially the cases for diaries, spells, letters which looks the same as any other common stuff. I always had to check (even read) through them one by one and still don't know how long I have to hold on to them. Until I came to use backpacks/pouches/crates/barrels to further catagorize my inventory, still, it is a frustrating work.
