Most RPGs leverage combat as a main source of mechanical conflict. From what I can tell, this tradition stems from RPG's heritage in tabletop war games, and to this day combat remains a staple of the RPG genre. The most salient example is probably Dungeons and Dragons, where character classes are almost entirely defined based on what they can do in a fight.
Many modern systems have introduced structured and engaging rules for social conflict, recognizing that role playing is a central element of RPGs and deserves mechanical support. The Duel of Wits system from Burning Wheel and pretty much the entire game of Hillfolk are good examples.
One aspect that has seen much less mechanical support is (environmental/wilderness) survival. Generally the rules for survival are condensed to the point of nearly being a non-mechanic. For example, in Mythras wilderness survival is essentially reduced to a set of timers based on a character's constitution.
What mechanics can be used to make the environment itself into a challenging (but not immediately deadly) adversary for the players? This question is asked in the context of the Mythras system (but not the Mythras setting), which is based on Basic Role Playing system.
For example, swapping out the Mythras inventory system for the one in Torchbearer would be a fairly straightforward change that could indirectly enhance the mechanics of survival by facilitating strategic resource planning for long journeys (e.g. is that crossbow a better use of a torso slot than a backpack full of rations?).
Please also feel free to suggest answers that do not port a mechanic from an existing system.