He can hold his breath for an extremely long time. So for short jaunts into near space, he needs no breathing apparatus, though he may need something to communicate with others if he’s not alone. With the Justice League, communication is usually handled telepathically courtesy of J’onn J’onnz.
In the late 1980s, there was the “Gangbuster” story arc, in which Superman was dressing up in a different costume (complete with helmet and visor/mask), calling himself Gangbuster and basically beating the living crap out of ordinary hoodlums. He was pretty much doing this in his sleep. Superman, becoming extremely annoyed with the fact that he couldn’t catch Gangbuster (because he definitely didn’t approve of his methods), eventually realized that he was Gangbuster himself. His subconscious mind had apparently become frustrated with having to hold back all the time when dealing with ordinary criminals and the fact that they seemed to get out of jail as fast as he could put them in. So something in his mind snapped, and he took on the Gangbuster persona.
I said all that to say this:
Realizing he was a danger to everybody else, Supes exiled himself from Earth. He set off into space, alone, intending to get as far as possible from other people so that he didn’t hurt anybody. He took along a breathing apparatus for the trip, because he didn’t know how long he would be in space, but he knew it would be way longer than he could hold his breath.
On another note re: the movie -
(I actually posted this last night, apparently at exactly the same time as the hardware malfunction, so it never showed up.)
I find myself wondering if the casting of James Marsden was intended to make a point. I’m a bit embarrassed to admit that I spent the entire first half of the movie asking myself, “Who is that guy, and where have I seen him before?”
Much debate has been made over the years regarding Superman’s Clark Kent disguise. Just how effective a disguise is a pair of glasses? General consensus: Not Much. And yet, it was Richard White’s lack of glasses that kept me from realizing right away, “Oh, it’s Cyclops!”
But it also occurs to me that the Clark Kent disguise isn’t just the glasses. It’s the whole demeanor. Clark Kent doesn’t carry himself like Superman. And Richard White didn’t carry himself like Scott Summers/Cyclops. So I was fooled, at least until halfway through the movie.