In most cases and most places,
the only really essential navigation device is a good map.
That is all I have used for over 30 years with plenty of off trail
travel and mountaineering.
There are definitely skills required to navigate with a map. These are best developed by experience in reading and using a map, especially a topographic map. Perhaps the most important comment that I can make here is the concept of "staying found". Follow your progress on the map! Don't expect to get confused and then be able to pull the map out and sort things out. This can certainly be done, but is going about things entirely backwards.
With decent map skills, in the western US, with prominent and distinctive topography, a good topographic map is all anyone needs. If you will be traveling in flat country with limited visibility, a GPS could be all but essential. This is not my use case. I am thinking of the Candian shield, Alaska, or other places without prominent visible landmarks.
Just recently I was taking off on a cross country passage in the California Sierras. We were chatting with a fellow on the JMT/PCT near our taking off point and told him what we were doing. He said, "Oh, well, no doubt you need a GPS to do something like that." We told him, "No, just a decent map".
Tom's backpacking pages / tom@mmto.org