Nine hours later...
Now I have the small problem that I can't remember what skills there were originally. I played almost enitrely with passive skills.
Rune stones or alchemical concoctions could be used for assault spells like Meteor Strike, Lightning and Poison Cloud (don't have a clue what it's really called). Holy Water for Bless. If lockpicking was free (ie. didn't require lockpicks), you could instead have lockpicks of various qualities. The only problem is that there are too many passive skills which you can't really have a one-use item for, unless it's a potion that lasts for a time. But then these bonuses are provided by equipment.
Oh, this feels far too hard to get right. (Maybe I just need sleep.) It worked in Diablo because the only skills you could acquire were spells. Divine Divinity is much too broad to simply include the same system. Though I would like to see books that teach skills in other Ways (of the Warrior/Survivor) as well. I remember seeing a screen shot of In-Between World where there was a skill book for one of the Warrior skills. It was an etched stone, like on the skill screen. I think it's a shame that idea was removed from the game.
Oh well. I need sleep. Good night!