Some headcanons for each of the playable characters from my SoloRPG, The Black Alder, which can be as canon as you feel like it:
Bruises is the youngest of a big family, and things are pretty unstable at home. He's one of the smallest boys in his grade. He's an incredibly angry, mouthy kid, and is constantly in fights at school. He was a ruthless bully to Boy Scout.
Braces has one little sister, and they get along great. He smokes too much weed, but all the teachers know he's a good kid. He gets away with a lot thanks to his sense of humor. He recently got his first car, and is hoping to get a summer job to help pay for it.
Running Shoes has an older brother who got the draft and never came home. His favorite past times are singing at church and running track and field. He worries constantly about making his parents proud, and doesn't know how he'll feel about someday being older than his brother ever got to be.
Crutches is an only child. He's obsessed with pop music, which his parents aren't thrilled about. He plays the electric organ at home, but only songs his parents approve of, which is often religious. He is the only Asian kid in most of his classes. He uses crutches due to post-polio syndrome.
Gold Chain has two little sisters. Half the reservation has a crush on him, and it's definitely gone to his head. His dad runs an auto shop which makes decent money, which Gold Chain helps out with, but only when he needs money for a date. Bruises is his nextdoor neighbor.
Boy Scout is an only child. For as long as he can remember, he's always been picked on for being a crybaby. In 1972 he got to attend the World Scouting Jamboree in Japan, which was the first time he ever left his home town. His parents argue often about him, because dad blames mom for raising a sissy.