Some targets on the battlefield may drop special items or tokens. They grant useful bonuses when cubed with the Class Charm you picked up in Kurast 3000 BA.

Veteran Tokens

In Terror and Destruction difficulty, you can find veteran monsters near the end of each Act. There are 5 types of veteran monsters, one for each Act.

Kill them and receive an 'Evil Eye' token :

Clawstorm Terror
Fairy Witch

Glowing Blob

Bane Hunter

Class Charm Upgraded [Class Charm] + each of the 5 tokens → Class Charm Upgraded returns [Class Charm] with added bonuses
This upgrade recipe adds the following bonuses:

+1 to [Your class] Skill Levels
+20% to Experience Gained