Columbus
The main character and the narrator of the movie, Columbus is a nerdy guy who hasn't spent much time outside prior to the zombie apocalypse. To survive the zombie attacks he made up a lot of rules to help him, including "double tap" and always fastening the seat belt.
Tallahassee
Tallahassee is a brawny character, who survived the apocalypse with his reckless bravery. He teams up with Columbus in search of a safe zone. Tallahassee is also on the search of the last Twinkies, and often mentions his puppy Buck, whom he lost.
Wichita
Columbus and Tallahassee accidentally stumble upon Wichita and her sister, and get tricked by the two, who take their car and weapons. Wichita is a grim character with trust issues, intent on keeping her sister alive, but she slowly begins to like and open up to Columbus.
Little Rock
Little Rock is Wichita's younger sister, and the two were always a team trying to survive, even before the apocalypse. Despite being very young, she is bold and doesn't get intimidated by the zombies.