Sokka will be the comic relief of the Gaang, as well as a tactician and warrior.  He's easily annoyed when things don't go to plan and complains quite a lot, but he can keep a level head when needed to.  He's also quite the ladies man, and tends to flirt with some of the women he meets.  He's usually at the centre of the Gaang's banter.  At first, he will take a dislike to Aang, but will see him as a friend later on.

Suggestions for the lines:

1 - At this point, Sokka is being held prisoner, and is shouting at Zuko who is trying his best to ignore Sokka's boasting and ranting.  Sokka is rather cocky and defiant at this point, and is trying to make himself sound like some sort of badass.

2 - Sokka is trying to get himself and Katara out of a trap, and when she starts water bending in order to do so he gets annoyed, thinking that she is wasting time practicing.  He's quite annoyed, and complains about how his sister and Aang spend most of their time practicing their bending skills instead of looking for food etc.

3 - Sokka is agitated as the last of the Gaang's food has been used and there's no nearby food to eat, so he is forced to go and find some elsewhere while Katara and Aang stay near their camp to do other chores.  Try to sound pissed off and demanding.