My last two shelves are filled with all my yarn. Originally, I only bought two shelves, but I vastly underestimated how much yarn I have when first buying them. With two shelves, some of my yarn would have to be squeezed into the same space as my needles, which I didn't like the idea of because it would just seem like a hassle that I'd have to remove all the yarn from the shelf before I can sift around for my needles, so that's when I decided I'd go back and get another third shelf so that I can separate them. Plus, it just looks neater that way.
Anyway, I'm sure there are neater ways to organize knitting material, but with my current funding, I think this is the best I can do. At the very least, things aren't shoved into random go-green bags anymore. Everything is in one place, nothing just falls out easily, and I can figure out a neater way to specifically organize my needles later. Furthermore, if/when my yarn collection grows, I can easily just keep adding more shelves And, maybe if I have enough yarn in the future, it'll be worth it to organize my yarn by its weight and colour or something. Until then, I think this will work out just fine for now!