First, the "striped pajamas" ellicit the most obvious emotional response. The boy outside the fence believes that they are pajamas, portraying the beautiful innocence of youth. However, the reader is aware that the pajamas are not pajamas but his outfit is actually a prison suit--showing the insensitivity of the Nazi regime to children and the naiivety of the little boy.
Secondly, the father's uniform ellicits an emotional response. Examine the line, "You wear the right outfit and you feel like the person you’re pretending to be". For Bruno's father, this is true. He doesn't completely feel like a man unless he's in that all powerful uniform--we can sense that in his character. Whenever he wears his uniform he is unusually cold toward his family.
The final outfit can be argued two ways. First, it can be argued that the outfit Bruno puts on to help Shmuel is the third outfit. It can also be argued that Bruno's normal every day outfit is the third outfit. I tend to argue that it is the latter. My reasoning, is that the first option is too similar to Shmuel's outfit. However, Bruno's every day outfit somehow mirrors his fathers--they seem very similar in color and style (except for the pants). But when he changes into Shmuel's outfit, we realize that Bruno still has an adaptability that his father lacks. His father's outfit has made him who he is. Bruno still has not been concretely defined.