A map and compass (and the skills to use them!) allow a person to find their way across a wilderness area without relying on GPS or cell phone maps, which can fail in many ways.
There are many different types of maps, but the most practical for wilderness travel is a Topographic Map, which shows both lateral and vertical scale through the use of contour lines.
Like maps, there are many different kinds of compasses, but an orienteering compass, with a clear plastic base that you can overlay on a map, is best for wilderness travel.