It said above (24:36) that Avraham gave to Yitzchak all that he owned. Why did the Torah repeat this here?
Rashi: It includes Birkas Daitiki, with reference to the Berachah that Hashem gave to Avraham, enabling him to bless whoever he wished. 1
R. Chaim Paltiel: Before, Avraham gave the permanent rights to the property, but kept the Peros for himself. Now he gave even the Peros.
Avraham lived 35 years after he sent Eliezer. He had acquired more property during that time. (PF) 2 .
Sanhedrin, 91a: When Alexander the Great convened an international Tribunal, the Bnei Yishmael and the Bnei Keturah 3 claimed that they too, were sons of Avraham, and that therefore, Eretz Kena'an belonged to them as well as to Yisrael. Gevihah ben Pesisa (Yisrael's spokesman) citing the current two Pesukim, pointed out that, apart from specific gifts that he gave to them, he gave all that he owned
Why did he give everything to Yitzchak? One should not divert inheritance, even from a bad son to a good son (Kesuvos 53a)!
Rosh, Moshav Zekenim (10) #1: Avraham and Yishmael were converts. A convert does not inherit a convert. Da'as Zekenim and Hadar Zekenim add that Avraham already gave everything to Yitzchak (24:36) before Bnei Keturah were born. 1
R. Chaim Paltiel, Moshav Zekenim (10) #2: Sarah had said (21:10) that Hagar's son will not inherit with Yitzchak, and Hashem told Avraham to heed her. Avraham learned from "Ki v'Yitzchak Yikarei Lecha Zara" that only Yitzchak should inherit (Kli Yakar).