Verse 25:33 implies that Esav sold the birthright for lentil stew. Why does it say that Yaakov also gave him bread?
Oznayim la'Torah: Because Esav might have argued later that the sale was invalid since he was forced to agree to the sale due to life-threatening hunger. Therefore, Yaakov gave to him bread, and after 1 he ate and was satiated, he sold his Bechorah for the stew, demonstrating that he sold it due to contempt of the Bechorah.
Alshich: He was teaching him that it is gluttonous to pour the cooked food down his throat without bread, like one feeds camels. Rather, he should eat slowly with bread, like people.
Are bread and lentil stew fitting payment for the Bechorah?
Maharal (Netzach Yisrael Ch. 15, p. 89): Esav wanted to sell the Bechorah due to his physical nature (i.e. he had no desire for Kedushah). He therefore received payment in material terms.
What does "and Esav despised the Bechorah" teach us that we did not already know?
Rashi: He disparaged Avodas HaSh-m. 1 This teaches us just how evil a character he was.
Seforno: Even after selling the Bechorah, he continued to consider it of no importance and not worth the price that Yaakov paid for it - which teaches us in turn, that Yaakov was not guilty of cheating Esav.
Ramban: The Pasuk is informing us why Esav was burned so badly on account of the Bechorah, as the Pasuk says in Mishlei (13:13) "He who scorns something will ultimately be injured by it."
Rashbam: The Torah tells us now how he despised the Bechorah, as a prelude to the story later, where he changed his mind and complained bitterly to his father "He took my birthright!"
Da'as Zekenim: It teaches that even before this, 2 he despised the Bechorah.
Ohr ha'Chayim, Malbim: This shows that the sale was not amidst duress of dire hunger. Also after he ate, he disparaged the Bechorah.
Ha'amek Davar: Esav openly held that honor does not depend on order of birth, rather, on attributes. Many non-Jewish leaders held like this.
Why did Esav despise the Bechorah?
Refer to 25:32:1.
Ibn Ezra: Because at that time, Yitzchak was poor, and he saw no financial advantage in being a firstborn. 1
Maharal (Ohr Chadash, p. 130): Esav himself is "disgraced" (Ovadyah 1:2), and as such he disgraces others.
See Ibn Ezra inside. The Ramban, who vehemently disagrees with him, maintains that the Avos, with whom kings made pacts, were Divinely blessed with wealth and honor all their lives.
QUESTIONS ON RASHI
Rashi writes: "The verse testifies to Esav's wickedness; that he disdained HaSh-m's service." Why does Rashi add that "the verse testifies"?
Gur Aryeh: This disdain was only in Esav's heart [i.e. he did not demonstrate it externally]. The verse tells us b'Ru'ach ha'Kodesh what his true feelings were.