I still have much to learn, I haven't tried everything, and this is all based on my personal preference but the following is all my favorite supplies I am currently using for my Bullet Journal.
Lemome Notebook
is by far my favorite notebook I have ever used. It is only around 10 bucks normally on Amazon (about half the fancier notebooks) and the paper is so nice and thick. Ghosting is almost a non-issuse. Has everything standard you would want in a Bujo like a pen loop, back pocket, stretchy band... etc. I will keep ordering it even though it doesn't have very interesting covers. What are stickers and shit for anyway, right?
Yoobi Pencil Case
has a ton of pencil case options that I love. They are easily portable, you can find them at Target, and every purchase with Yoobi helps schools. Sounds like a good thing all around to me.
Jayden Apple Stencils are the best. I have a few other stencils but I really don't need any other ones than these since they have rulers and stuff built in. I do everything pretty custom though so I am not much of a person that needs stencils extensively. Also, it came with a little felt case!
I found these silly little pencil cases on Aliexpress (any crafter or bullet journal-er should have this app, it's the best.) They aren't too big but I keep some washi, scissors, glue, and stickers in here. I mostly like how they look.
More supply posts in the future to come!