What made the boys feel like heroes?

Are you sure you mean chapter 6? I think you mean chapter 13. Around midnight, Tom "the Black Avenger of the Spanish Main," Joe Harper "Terror of the Red Seas," and Huck Finn "the Red-Handed" meet by the bank of the river with stolen goods: a skillet, ham, tobacco, bacon, and other trifles. By raft, the gang of three drift toward Jackson's Island. After landing safely and setting up "camp," the boys contemplate the desirable lifestyle of pirates.