Cheerleaders didn't walk around like that all the time at my HS, but some days they would if they were practicing after school (or there was a game later on). A number of the jocks wore their jackets more often than not. I don't remember how many pep rallies we had a year though - at least a few. I didn't always go to them.
Knowing which films/tv shows you are thinking of would help because some overdo it or are straight up parodies while others may be based off of memories of a HS not representative of most.
I sincerely hope CrabCake doesn't have 'Ferris Bueller's Day Off' in mind:
https://www.youtube.com/watch?v=91oESPRinas
Awesome comedy though it was.
Clearly Danger 5 is the most accurate representation of American high school:
https://www.youtube.com/watch?v=zW9HdRjD4eo
Loved that show. They ever go beyond a second season?