As far as small pocket organisers go, the Compact Pen Case from Lihit Lab is pretty small! Despite its size, the well-thought-out layout of its pockets ensures you'll be able to carry a decent number of pens, as well as other items like a mini notebook, Post-Its, a pencil sharpener, eraser etc. On both sides of the case, there's a large pouch that could comfortably hold a large mobile phone.
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