Benyamin, while being quite young at the time, is notably missing when Yosef is sold. Does he deserve a reward for not participating or was he simply not included and therefore is incidental in the story? The only way I can figure to determine the answer to this question is to determine if he in fact did receive a reward. Therefore...Did Benyamin receive a reward for not having participated sale of Yosef?
According the Chida, who says it in the name of the Rokeach (Brought in Vedibarta Bam):
According to an opinion in the Gemara (Gittin 43a), when one sells a Jew as a slave to a non-Jew, he is fined to redeem him for up to 100 times his value. In the Torah we find a slave to be valued at 30 silver pieces (Shemot 21:32). Since Yosef was sold as a slave to an Egyptian family, it would cost as much as 3000 silver pieces to redeem him.
Since 10 brothers played a part in his becoming a slave, each one would have to pay 300 silver pieces. Consequently, when each of the brothers was deprived of 300 silver pieces, it was as though they paid their fine. Binyamin took no part whatsoever in the selling, so Yosef gave him 300 silver pieces.
So, while it wasn't a reward, Yosef gave only Binyamin 300 silver pieces, so that the other brothers, who did sell him, would lose out on 300 silver pieces. This would take place of the fine they halachically owed.
As @Alex pointed out in the comments, the Torah Sheleimah brings this idea down in the name of many Rishonim.