Here is how my experience has went so far:
Clothing Brands=It seems to me that more people wear what they want instead of trying to by the cool brands, also I noticed that not as many people find wearing the name of a brand on their shirt cool.
Kids get picked on=Anyone can, but at my school the kids who smell bad get picked on pretty bad, but hey, they should take a shower once in a while LOL, but remember it isn't nice to pick on kids, don't just do it cause other people are. Just be yourself, I promise it is the best for you!
Food=Depends on your school, but mine is the same because the Junior High and High School for my district share the same cafeteria, but I noticed that the other nicer schools in my area have way more variety than my school which just serves the basic meal and a chocolate milk box, it's boring.
Social Scene=For me, my cheer competitions, what ever season it is I Like to go watch the sports teams for my school, the maLL, movies, a friends house, the occasional party, I'm not a big party goer though, because there is usually beer and I don't want to get into trouble, so stay away from those parties, u can get arrested for just being there.
Sex=The only way to put it really is that some people are a virgin and some are not. I would definitely say that more people have sex in high school and there is more pressure for it, but don't get dragged into doing something your not ready for, I'm a virgin and nobody could care less, respect yourself and people respect you, it's not like they will go around making fun of u for being a virgin.
Dating=Pretty much the same as Junior High, but you will probably see more serious relationships, and there are more things to do and places to go, depending on what your parents let you do.
I was scared for my 1st day, and the whole day kinda goes like a blur, but u get used to it in Like 2 weeks, then it seems like u have been there forever, but my experience has been pretty good so far, I'm just trying to make the best of it=]