This question came up recently, and the immediate answer that I got from people around me is that Yaakov was securing the brachos which are due to the bechor.
However, the problem with this answer is that ultimately, having bought the bechora did not actually help in obtaining the brachos. After all, instead of doing any trickery, Yaakov could have simply went over to Yitzchak and told him that he had bought the bechora and was therefore entitled to the brachos.
Others mentioned the idea of being entitled to bring korbanos. Once again, I don't see the connection between being a bechor and bringing a korban. After all, all the avos brought korbanos as well, and none of them were a bechor.
So my question is, why was Yaakov so interested in acquiring the Bechora from Eisav? What did he ultimately gain (or attempt to gain) from the purchase?