saw on a homesteading type video the guy had a handy dandy "stump vice" for field sharpening - going to be looking for a future buy - hammers into the stump - locks onto the bar for steady hold ....
second thing he was pushing was a "two in one" manual file holder - built specific for your chain - holder has two files being held in position for a full chain section sharpening - another timesaver to check on ....
third - he had a "Woodsman" tool for quick log cut-off determination - simple as hell but great if you want max length but don't want firebox problems with overlengths ....
For my personal rule/use:
I don't do field sharpening. I carry an extra blade, in the box it came in. It gets dull, or hit a nail, or in one case a rail road spike ( deep in a tree??? Where are those sparks coming from????) and just change it out. For me, it takes less time than sharpening.
Bought an electric chain saw sharpener from Harbor Freight for 30.00, and a couple of extra wheels, and that thing does a great job, so long as you take it easy and don't burn the points.
I don't do so good with a file, and cutting a straight line. A near expert at using a file to make it cut in a curve.
After dulling everything, take an afternoon and sharpen blades for saws and mowers, which I use a different grinder on.
BTW the crew that came and cut my huge Water Oak, and stump ground it and cleared it, the old man used a file on his 3 foot Stihl, to sharpen it. Did it while the rest were topping out the tree. Still took him a while. The base where they left the stump was 74", at the widest.
Every saw they had, and they had several, was a Stihl. And they do it for a living.