A player using "Interact".
The interact tool is the most important feature of Apocalypse Rising. It is needed for basically everything, from simple looting to fixing a vehicle.
Significance
The interact tool is important because it is the main tool of the game. You need it to pick up food and drinks, to pick up guns for defense, and to pick up backpacks for more inventory slots. If you didn't have the tool, you would either:
a) Die of thirst/hunger.
b) Getting shot by a player and not being able to return fire.
c) Get rundown by a horde.