If you know what you're doing, I genuinely believe you could carry just what I carry everyday to school (started this after my bookbag that i had for 3+ years broke):
All the paper I need is in here and the heaviest 2 parts are actually just the mathbook and chromebooks i have to carry around. Now a lot of the classes force chromebooks anyways for the few times you actually do something of any value (or even of non-value), and those that don't often keep the books in the classroom (such as English I) which keep them because the kids destroy it. My high-school doesn't even have 700 people despite being an American public high-school, and even in bigger schools I'd imagine you might still be able to do something like this.
If you have a good jacket and your school doesn't ban them, just carry useless stuff in your pockets. I carry a pencil sharpener in my bottom-left pocket, a roll of toilet paper + some plastic bags in my bottom-right, and money in my last pocket at the top, putting it there so its harder to steal it or even notice without me taking it out my pocket (seriously, I'll notice it then just beat them senselessly, if i can get away with it I'll even stab them with my pencils because I've got plenty, probably enough for my entire grade and then some).
I then carry 2 pencils in my left shorts pocket and on the right, it just depends. Sometimes I bring nothing, other times my phone (usually off ofc, but i disable notifications already except for iMessage, where i rarely get anything). I've considered to not bring my phone to school since it may be possible for them to justify searching the contents if they suspect anything, though I could just use Firefox Focus and login to my emails if I needed to check it anyways, which I also kinda already do so eh whatever.
I can carry basically nothing to school, yet do fine. As much as I hate the digital stuff because its inconvenient in using it sometimes, its much better not having to carry around a ton of paper and textbooks, along with some of the classes having teachers who don't even care and just let everyone Google everything. I doubt there's anyone else who's 14 here and especially not those who are in 8th or younger still, but if there is somehow, absolutely try to cut down on what you have to carry.
If you happen to have classes on another side of the place (such as both of my 4th hour classes on A and B days), you can actually get there without having to risk being late nor running out of breath trying to run across the whole damn place. Its very convenient, I could probably turn this into an entire article on my website. Might honestly do it and call the link "hs-minimalist.html", would likely actually be of more help than my last actual note-worthy one that boiled down to "cash gud, digital bad" (yes its true, but still).