For me, it'd probably be my portable battery pack. I didn't realize how much I needed it until I was stuck with a dead phone at a bus stop past midnight (a.k.a. no more buses). There would be... several other instances of this...
Other than that, I really love this eraser stick. The tip is super fine and perfect for erasing small details on pencil drawings.
![](https://www.cultpens.com/imgs/products/cp/950_constW/TM12075-STR~Tombow-Mono-Zero-Eraser-Fine-Striped_P1.jpg)
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