The easiest connection that can be drawn between other texts and Huckleberry Finn is that of its prequel, Tom Sawyer. The books even share some of the same characters. Interested students should pick this up as their first supplementary text.
Other than reading more Twain, students may also want to read other American novels with similar themes, whether it is of travel, such as Kerouac's On the Road, or coming of age, such as Crane's The Red Badge of Courage. London's The Call of the Wild may also be recommended as an ancillary text.