There isn't too many such things that I know of. The milking contest in Gwendy's farm increases dex, the random encounter at crossroads and king's road with the patrol asking you if your adventurers or bandits will increase charisma if you choose adventurers, likewise the random encounter in crossroads and king's roads about finding the bandits increases charisma if you choose the extort option. Those are all that I can think of, and all of those have a cap to how high they can raise the stat in question. Also as the above poster mentioned, the various transformative potions raise some stats, though I believe its usually a trade-off, as in they raise some stat and lower another, and I also think that if you drink too many of them you will bad end, at least Miranda warns about losing your mind if you overuse them in one of the early meetings (explaining how the wolves in the forest used to be people that drank too many of those potions).