What’s the bare minimum you need to navigate across land?  For most people, that would be a compass and map.  A basic road map is sufficient to get a rough approximation of the lay of the land.  More detailed relief maps can help plan for elevation and estimate possible water sources but they also take up more room in your pack.  Waterproofed or laminated maps are also extremely helpful.  Lensatic compasses are the most reliable for little money.  If possible, a compass and protractor are also extremely helpful for route planning.  Obviously, not as essential but nonetheless useful.