I keep a couple 20mm button compasses with me most every day. In my job I might start a day in a motel, but end the day a 100 miles away searching for receivers or shot points in the densest thicket imaginable in the absolute middle of nowhere (just me, my machete and Big Foot). All I need is a general idea of true north and I can generally locate the lines and points (miles from nowhere) and when through, can generally meander my way back to my vehicle on some overgrown logging road before the sun completely sets. I loose these tiny compasses all the time (maybe one or two a week). Be sure to purchase the liquid filled Grade AAs. I purchase them six dozen at a time. They are much better quality than the Grade As for numerous reasons, but to me its mostly because the Grade AAs are more heat tolerant if left in a car on a summer day. When I'm in unfamiliar cities I use them when on foot trying to orient so as to locate a Starbucks or some shade tree attorney's office. However I always go a little out of my way to find a road that I'm reasonably certain runs due North and South and check the button compass's declination for that area. (Good roads to use for determining declination are harder to find than you may think. It's best to ask a local surveyor to tell you which local road or road segment comes closet to running true North and South.) Just remember to check it a couple times before you start depending on it in the woods or in the city --- to rule out outside influences.

By far the best button compasses in my view are the Nato ones. However, there extraordinarily expensive (expensive as all get out) and hard to come by. In any case, every member of my family keeps one of these Nato compasses with them in their PSKs.

As for key chain compasses, in my view the best in the business is the machined solid brass 150C Tru-Nord Key Chain model. What really separates the US made Tru-Nords from the European (Scandinavian) pack is that the Tru-Nords are compensated at the factory for the zip code where the key chain compass is to be used. When I work on projects outside of the USA, I just send Tru-Nord the Lat & Lon of where it will be used and they quickly have a new compensated one delivered to my door step. When using the Tru-Nord, you get true north only without having to fret over declination - although there's nothing they can do about the wobble of the earth. I have a drawer full of the factory compensated Tru-Nords, each tagged by location. They're my work horses on all my major field projects. They're light but built like tanks. High end in every respect.