In high school, I usually carried my books & everything I needed for like my 1st two periods, then I would go to my locker and switch stuff out, and I would continue doing that for the rest of the day. I mainly did this because our lockers were assigned by what class we were graduating in & they never changed the whole time we were in high school & where my classes lockers were located were convenient being on the first floor so we could at least always switch out things during our lunch period if we didn't have time to during the day for whatever reason (our lunch room was just a big common area, which was also the main area to walk between classes on the 1st floor).
Now being in college, I typically carry my books because my classes are typically only 1 day a week & I only have a book or two (but the classes are like 4-5 hours long, which makes me wish they were twice a week sometimes). I also have a big portfolio type thing I have to take to one of my classes weekly that wouldn't even begin to fit in anything. I do have a JanSport backpack too (that's really cute & neon cause I'm kind of obsessed with neon colors), but I only tend to take that if it's raining or snowing & I don't want to get my books, papers, projects, etc. wet because it could ruin them or if it's been snowing/sleeting and is really slippery because then it's just easier.