Puzzle-in-a-book treasure hunts and BOTG (boots-on-the-ground) puzzle communities often end up with a working Google Maps list, decoded coordinates pinned as you solve, candidate locations to rule out, spots other solvers have shared. None of that is useful once you're actually standing in a field with no signal, unless it's already on a device that doesn't need one.
MapsLinkQuest converts that list straight into a GPX file. Paste the share link, download the file, and load it onto a Garmin, into Gaia GPS, OnX, or any other GPS app before you head out. Every candidate location comes with you, named exactly as you labeled it on the list.
This is especially useful for narrowing down a search: keep a running list of every coordinate you've decoded or ruled out, share it with your hunting partners via the same list link, and everyone's GPS shows the same set of points without anyone re-typing coordinates by hand.
Got a list from another searcher? The shared list page covers exporting one you didn't make.