Here is the truth: you don’t need more than a notebook and a pen to keep a bullet journal. You really don’t. However, some tools can still be really useful for making your bullet journal more personal and most importantly, to boost your productivity — the whole goal of keeping a bullet journal in the first place.
When the inside of my bullet journal is just a sea of black text on white paper, I get lost. I’m a visual thinker, which means I process things more quickly if they’re made visual. I color-code so I can see at a glance what area of my life a task or event relates to, and I use colored markers to fill in habit trackers and highlight important information.