A Bio Upgrade.
Your body can tolerate temperatures from -20 to 60 ºC and your heat signature blends with the environment and is indistinguishable from it.
Additionally, you can hibernate for periods of time of up to 1 week per Constitution point. During hibernation, you cannot do anything, but you do not need to eat or drink and you only needs half the regular amount of oxygen. Suffering damage or other extreme sensorial disturbances can wake you up.