Player > Feats > Toughness
You have enhanced physical resilience, and harsh conditions or long exertions don’t easily tire you.
For every character level you have (and whenever you gain a new level), you gain 1 Stamina Point. In addition, you gain a +4 bonus to Constitution checks to continue running, to avoid damage from a forced march, to hold your breath, and to avoid damage from starvation or thirst. You also gain a +4 bonus to Fortitude saving throws to avoid taking damage from hot or cold environments, to withstand the harmful effects of thick and thin atmospheres, to avoid choking when breathing in heavy smoke, and to avoid fatigue caused by sleep deprivation.