The Hunger Games by Suzanne Collins deals with a multitude of themes.
Violence--Although violence is a key component of The Hunger Games, Collins uses the construct of violence to criticize the sensationalism of violence through media.
Sacrifice--The idea of sacrifice plays a significant role from the moment Katniss volunteers herself for Prim to the moment with the berries. Collins offers several variations on the meaning of sacrifice.
Trust-- Trust becomes key in the novel when Katniss finds that she no longer knows who to trust.
Love-- Many of the characters' actions, including Katniss', are motivated by feelings of love and a desire to protect. Many of Peeta's decisions before and during the Games came from a desire to protect or help Katniss.
Some themes can include sacrifice, trust, love, etc. Katniss had to sacrifice so much going into the Hunger Games knowing there was a chance she wouldn't come back, she went away from Gale, her mother, her sister, yet she saved her sister with her life. Trust, Peeta. Peeta kept Katniss safe and made sure she would not die, he could have killed her but he loved her too much and kept true to that. Love, Katniss and her family, Katniss and Rue, Katniss and Peeta, and Katniss and Gale. All these emotions affected her greatly and the book and had great messages.