Tools of Characterization
Or the lack thereof. As Siddhartha tells Kamaswami, the ability to fast in Siddhartha is viewed in a positive light because it teaches independence and patience. Those who are capable of fasting are not easily persuaded to perform various acts or services in return for food.
Kamaswami lives in a big house. Kamala basically lives in her pleasure-garden. The Samanas wander in the most painful locations they can find. Vasudeva lives in a hut by the river.
Call us crazy, but it seems that the characters’ habitation reflects their natures. The guy concerned with money (Kamaswami) lives in a big house while the woman concerned with pleasure (Kamala) lives in a pleasure-garden. The ascetics and enlightened follow Jack-from-Titanic's adage of "If you got nothing, you got nothing to lose."
Siddhartha basically looks like a god among men. He's, well, hot. We’re not even given a physical description of Govinda, which helps establish Siddhartha as the guy we’re interested in... both because his good looks turn our heads and because he's a compelling protagonist.
Thoughts and Opinions
Siddhartha has lots of independent thoughts—as in, he’s an independent learner. He prefers seeking enlightenment from a river rather than from Gotama Buddha. Govinda, in contrast, comes across as a bit of a parrot sometimes. His willingness to follow the teachings of others reflects his "follower" and "sidekick" character.