There are many examples of friendship in Collins' novel The Hunger Games.
First, the friendship between Katniss and Gale. This friendship exists because they both have specific talents that they can use to help each other to survive.
Second, the friendship between Katniss and Rue exists because they come to realize that they can take part in the Games, create a bond (outside of the Careers), and look to each other for support.
Lastly, the friendship between Katniss and Peeta exist given they both realize that striking the friendship up is the only thing that will insure their survival. Katniss does not agree with the Games and she knows that the relationship between them will do one of two things: insure their lives or make them enemies of the Capitol. Regardless, the friendship is what is needed to survive in either circumstance.
The pacts made within the Hunger Games could be used as an example. In the second book, the participants form pacts to ensure their safety as well as their life. If you are talking from parts within the book Katniss and Gale is a friendship that has always been their where they have always been there for one another and soon turned into love and Peeta and Katniss turned into a bond of protection to a bond of trust and true love. But one of the most prolific friendships I saw was that of Katniss and Rue's. She protected Rue and they were with each other as supports.