Spending Resources During a Rest

If a feature is expended while resting, that rest cannot recover a use of that feature. This does not apply to hit dice during long rests, or resource pools (unless over half of that pool is expended over the duration of the rest).

Rest Penalties (optional rule for survival gameplay)

Field rests being taken in uncomfortable environments can lead to fitful sleep, and exhaustion. These uncomfortable environmental factors are called rest penalties. 

• At the end of a field rest where you are subjected to rest penalties (but before you recover resources or levels of exhaustion) you must succeed on a DC10 Constitution saving throw. If you fail, you gain a level of exhaustion.
• If you are being subjected to more than one rest penalty, during the field rest, the DC of the Constitution saving throw increases by 2 for each rest penalty past the first.
• Rest penalties include, but are not limited to: 
  • Sleeping in too hot/cold of an environment, sleeping without cover in a storm, going to bed hungry, sleeping in armor, or resting in a dirty place.