Combat Endurance

Your countless battles have hardened you to the point of having an extended endurance. You gain the following benefits.

When you complete a short rest and roll hit dice to recover hit points, you can roll a hit die twice and choose the higher result.
When you complete a long rest, you recover all expended hit die.
You have advantage on Constitution checks and saving throws to avoid exhaustion.
When you take damage, you can use your reaction to expend and roll a hit die. You
recover hit points equal to the roll.