Paper
Fountain Pens! (Of course...!)
My brands of choice here are Diamine (affordable, great quality and come in a fantastic range of colours), Sailor and Pilot (not pictured). I have one of the massive bottles of Pilot blue-black ink which I use to top up my work pen; alternating it with a Diamine work appropriate offering.
Coloured Pens
I feel like one cannot have a bujo arsenal without including Tombow brush pens and Staedtler fineliners. Tombow brush pens have replaced Zebra Mildliners as my highlighters of choice too. Both of these pens mentioned look great in my bujo - not too bright or garish and just the right amount of colour to add a bit of interest to the pages.
Monotone Pens
Of course Muji have to make an appearance here - their gel pens are a staple and having been using them for the last 16 and a half years, they had to be included. The Unipin finaliser is also great for those doodles and setting up of pages. Highlighting anything written with the Unipin fineliner is great because the ink doesn't smudge.
Other Random Bits
Kraft paper adds a bit of texture to my pages and I like how white ink looks on it. I've also been experimenting with black paper too which I quite like. It adds a nice contrast to the white pages of my bujo.