To earn the Collector Achievement in "Fable II" players must acquire 20 items from locations around the world that comprise the inventory of Knothole Island's Box of Secrets Shop. The items range in rarity, trade value, and each has a reward associated with its being found.
According to XBoxAchievements.com, the items one needs in order to unlock the Collector Achievement are the Regal Purple Dye, 2 Crucible Peanuts, 3 Crunchy Chicks, 2 Lutes, 1 Monk's Robe, 2 copies of "Murgo's Big Book of Trading," 1 Pure Experience Extract, 1 Diamond, 1 Eternal Love Ring, the book "Marriage and How to Survive It," 1 Pretty Necklace, 2 Puny Carrots, and 2 bottles of Table Wine. XBoxAchievements.com also lists the location, reward, and economy rating of each item on the list. Some items, like the Crunchy Chicks can be acquired in regions with very low economy ratings, but the economy rating of a region needs to be improved in order for them to stock items like the Regal Purple Dye.
Among the many unlockable achievements for the video game "Fable II," several have to do with finding objects scattered throughout the world. AchievementUnlocked.net has a list of other achievements that can be unlocked in "Fable II." There, other collection and non-collection achievement guides can be found.