I’ve used composition notebooks, 3-ring binders with or without sheet protector sleeves, some hardback sketchbooks that I wrote in with calligraphy pens , fountain pens and markers, colored pencils and acrylic paint, last year I got a couple old fashioned looking deckle edge cotton paper notebooks from amazon.
I have random notebooks to keep track of different projects, like one is strictly for runes, another for card reading, etc.
There’s nothing wrong with compartmentalization, I have to second what Greyhoss said, if you think everything needs to be in one volume you’re going to end up with a lot of volumes anyway, and they might be almost impossible to use because everything is so crammed into one volume.
Amazon has a lot of great blank notebooks, whether lined like journals or sketchbooks. They run the price from 5-7 USD each down to 1-3 USD if you get a bulk purchase. Stores like Office Depot and staples always have some nice journal type books, but they’re more expensive, they’re probably ordered off Amazon too jajaja. I’ve got some nice ones from Walmart and the dollar store too.
i saw a cool video on YouTube where this one lady made a book of shadows with brown paper grocery bags, it looked really cool, different, handmade. It was huge too, it probably would take me a decade to fill that up.
in a reference to ye olden tymes of thee magickal arte, a lot of those were written in really small books or manuscripts with vellum/parchment folios. Like 5x8 inches. Tiny. Just for some perspective.