Just started playing this game again (nostalgia overload - thanks GoG), and a decent amount of my memory has come back relating to the early parts of the game...but I'm at a loss when it comes to certain items. Namely, skill books (The Optics Primer, Acute Senses and Perception, etc.) and quest items ('Notes' from Scott in Aspreza, 'Handkerchief' from 'the witch' near Sortiga, etc.). Once they've been used towards w/e purpose, they don't disappear, and seem to serve no further purpose - they can't be sold to any merchant I've found, nor given back to their rightful owners...so I'm at a loss as to what I should do with them. Have them all stored in a specific abandoned house, atm...

Edit: Partial solution - completely forgot about the scribe in Panizo; able to sell all books to him (even the 'Notes' for 1 gold). Still no idea what to do with the handkerchief though...

I'm not sure about the handkerchief, but I believe that some of the skill books may come in useful when you reach chapter 5 when Raal is in the party. You'll need to keep them in Kaelyn's inventory when she leaves at the start of chapter 4, and the last chance you'll have to go back and reacquire them from the vendor is before ending chapter 2 (although IIRC there are one or two books in chapter 3 as well).