I understand most of this because I have friends I visit quite often who have multiple kids of varying ages and have seen most of this played out in real life..
Yes, that's pretty much what swag means, but it doesn't have to be free, just clothing/accessory merchandise of some sort. Kinda the way someone presents themselves, really. So, someone's swag could be: Flat-billed baseball cap sideways, wearing running pants halfway down the butt, having like 20 chain necklaces of different length around the neck, and rockin' the tank top, while always walking with a shoulder leaned and talkin' like a thug even though they live in Beverly Hills.
And YOLO is effectively a short way to say "Carpe Diem" and is terribly overused in current teen culture for doing something stupid, but not regretting it. In context, you could say "Dude, totaaally broke my leg and ruined my swag trying to dive from the balcony into the pool but hit the bushes, but y'know, YOLO, brah."
Hash tags used outside of Twitter is increasingly common as well. My friends' kids like to do it quite often, even in verbally.. her child once said in response to having to do chores "hash Ihateyoumom".
The blackboard was an easy way to ref current music, where in hip hop, almost every single seems to feature (abbreviated feat.) another artist.
Tight pants for guys and flipped up baseball cap bills with words on the bottom or just flattened with a price sticker are a trendy clothing fashion these days for kids..
Yeah. she just threw as many trendy memes/styles as she could find into one comic strip to make it appeal to the teens. Such as a marketer would be apt to try for getting those teens to purchase merch and increase hits for adverts.
edit: wanted to clarify a couple points and holy typos batman..