I don't recall my first day of high school at all. But that's likely because I went to school on the same campus from 5th grade to 12th grade. In middle school, most classes were in the middle school building, but by 7th and 8th grade we had classes in some of the same buildings as the high school so there was never really any change for me in the transition from middle school to high school.
We all ate in the same cafeteria at the same time and there was a snack place where both the high school students and middle school would go.