What are some character traits Doug shows?

Doug is loyal and loving; he is especially considerate to his mother because he knows that she often bears the full brunt of his father's bad temper.

She went back to the pots, all lined up on the front porch and she took three in her arms and carried them to the McCall house next door. Then she came back, took up another three, and carried them across the street to the Petronis. When she came back again, I started up to the porch to help but my father smacked me on the shoulder. "If she wants to do it, let her do it herself," he said. 

In the above quote, Doug and his family are moving to Marysville. Accordingly, Ernie Eco, a ne'er do well friend of Mr. Swieteck (Doug's father), has promised to get the latter a job at the Ballard Paper Mill. The text tells us that Doug wanted to help his mother move the heavy flower pots but was prevented from doing so by his father. Doug's loving and loyal nature is clearly demonstrated by his actions.
Doug is also brave and determined. Despite the physical and emotional abuse he suffers at his father's hands, Doug refuses to be intimidated by him. When his father yells at his mother for failing to fix lunch, Doug stands up for his mother:

I told him we didn't have lunch yet because how were we supposed to know where Spicer's Deli was and he had taken the car anyway and Mom had to clean up the kitchen because he sure wouldn't have wanted to eat in this dump before she did that.

Doug's answer is both courageous and proactive. In speaking out for his mother, he absorbs the brunt of his father's anger so that his mother is spared from pain. Doug's words and actions in both quotes show that he is loyal, loving, courageous, and proactive.