I do mountain bike (and thus indirectly hiking) trail development, construction, and maintenance as volunteer work. This has shown me a surprisingly useful place for QR codes: on trailhead map boards. The code just links to a (well optimized) PDF of the map itself, along with some text that says "Scan this with your phone to download a copy of the map.".

It amazes me how many people I see scanning the QR code to get a copy of the map before they head out on the trails.