I keep one of these in the saw bucket for emergency use away from power. (And I keep two spare chains in the bucket so I do not have to use the file.)
I also have a bar mounted file guide. (Granberg File n Joint) It is the most accurate way to hand file a chain. Mine is Stihl brand. This link is Oregon brand. https://www.oregonproducts.com/en/File-Guide%2C-Bar-Mounted-Consumer/p/23820 The image will not transfer here.
It resembles my Stihl guide, but the Stihl has no plastic parts.