To get the right feeling of this era of time, we needed to find the perfect costumes, that would make no sense in military sense. They had to show that the characters are of military background, but that there wasn't a established military economy.
That is why the heroes in this movie carry military clothes of desert khaki material, and are also not size regulated. This further developes the image that the soldiers in this post apocalyptic time take on whatever clothing is available.
It was also important that each character had a distinctive look. The sarge, had a barret to show that he was the guy in charge. Harley and Mason have more neutral clothings, and yet distinctive in their own ways. Harley had a boney hat, which gives a sense of silky smooth red neck bad boy attitude. And Mason has a cap, which give his eyes a mysterious look. As if he carries a dark secret, which he does obviously.
And finally Rilco, who has a green military bandana, to show that he is the bad boy of the unit, which goes hand in hand with him being the newbie of the group, the guy who stands outside the group. Which is key in his development in the story.
Still all four have the same military clothing under, to show that they were a unit, and also part of a greater army, which can be seen in some sequences.
The riffles also play a role in their distinctive looks. For instance, Mason is a pillar of strength, and he therefor has the heaviest riffle. He also carries a pump riffle, which is massive in size and effect, which implodes in the characters ripple effect on the group.
