As it is unlikely for us to be able to create the amazing costumes that they have in super hero movies nowadays, I think it may be more appropriate to look at 'the hidden' life or the alter life the the heroes live.
This is Peter Parker from the spiderman movies, this is the kind of dress wear that he has on when he is out taking photos and being spiderman.
As you can see, as most superheroes like to blend in, he is wearing just normal everyday clothes. However, he is still wearing fairly smart clothes, but nothing too flashy. He looks nothing like a super hero guy would, he almost looks 'geeky' especially with the hair and the glasses.
This shows that we can still use everyday clothes in a superhero movie, especially if we stick to their 'secret' side of the story.
This is shown again through alter egos, for example Bruce Wayne who is Batman, Tony Stark who is Iron Man for example, they often wear suits but sometimes they do dress down, especially when they are not 'in their super hero status'. This is somthing we should definitely consider when creating our opening scenes.