Self-Sustenance was the ability to survive without air, water, food or sleep. This type of super power varies from person to person. Some characters may be able to survive without food, but not air, and so on.
This ability is useful for characters such as Superman, who can fly through outer space unprotected thanks to his ability that allows him not to need air to live. Keep in mind that this doesn't necessarily mean that Superman doesn't need to breathe, but it does seem to indicate that he can at least sustain himself without air for a lot longer period of time than a normal person.
In fact, persons with this ability have even been noted to communicate verbally in a complete vacuum, even though sound doesn't normally pass through the void of outer space. This seems to indicate they have at least a limited control of sound, and are able to "throw their voice" along with the air stored inside their bodies, in the direction of the person they are talking too, using sound manipulation and air manipulation as an advanced type of ventriloquism. It is also possible that Super Breath could be a factor in this power, rather than air manipulation, in fact this seems more likely. Even when engaged in an in-vacuum conversation in deep space, such a character doesn't seem to be low on air, therefore one can assume that characters with this ability can sustain themselves without air for a very long time--at least as long as their internal air supply remains.
- ↑ This is just conjecture based on the fact that in multiple episodes, Superman is seen talking in outer space and others can hear him, which in normal circumstances should be impossible, since sound cannot pass through a vacuum. However it should also be noted, that Superman does know ventriloquism, as has been established in the Filmation series, and referred to as "Super Ventriloquism."