I think the proposed challenge name is lame, so open to suggestions here.
You have two bars similar to those fatigue/drown bars that always decrease. One is hunger and another is thirst.
Thirst could deplete in 1 hour for instance, and hunger in 2 or 3. They are restored by consuming any drink/food (respectively) at the rate of the duration of the consumable. For instance 18 seconds of drinking water would gradually restore thirst at a rate of 100% / 18sec. (https://octowow.st/db/?item=159)
