In military parlance, "Level 3 - Sustainment". Water, shelter, and food appropriate to the environment in addition to backcountry travel tools. Multiday travel is focused on tuned weight conscious solutions and a very bare minimum of open ended "what if" tools. Here are three gear lists that comprise what one traveler carries for solo on and off trail backcountry travel:
Although this page contains information about the gear you might use, it is important to remember that there are two other equally important legs of the tripod - wisdom and efficacy. In order to travel safely and effectively, you will need to develop those other aspects moreso than you need to acquire gear. This 8 video (and growing) playlist from the HPG Longhouse series covers a variety of important multiday travel topics including land navigation, water procurement, and several others.
play_circle_outline Intro To Backpacking
Head knowledge is a start on wisdom, but it helps very little with efficacy. For that you need field time, which can be accelerated with classes from our recommended instructors.