I think it was Jon who clued me into the inherent impossibilities of Superman wearing his costume under his street clothes, but I can't for the life of me find the post where he mentioned it.
Anyway, my ultra-cool Superman 13" doll (yes, doll. Action figures don't typically come with a change of clothes) finally arrived, and I can now personally attest to the wardrobe difficulties that must plague Superman on a daily basis. Perhaps he stores his cape in a pocket someplace. Perhaps he keeps his belt and boots in a desk drawer. But there is no way that that man can wear a jumpsuit, briefs, a belt, a cape, and a pair of boots underneath socks, pants, a tucked-in shirt, the undershirt he'd require to keep that big red 'S' from showing through his white shirt, a belt, socks, and a pair of wingtips. It's simply not possible.
My theory? He wears the skintight shirt, possibly pants, possibly briefs (I'm not quite willing to concede that the pants and briefs are separate items) under his clothes. His boots are similar to Spider-Man's (no hard sole), and he keeps them folded up in a pocket or something. The belt's trickier, but the cape is folded up (through a method he learned from Barry Allen) in the buckle.
The figure itself is pretty cool. There are parts of the head sculpt that I'm not too keen on, and the coloring on his face makes him look a little sickly, and I can't figure out how the heck his feet are supposed to fit into his Clark-shoes (or, for that matter, how he's supposed to fit into his boxers). But overall? Freakin' awesome. He even comes with a copy of the Invasion! Daily Planet issue (the full-sized version of which I picked up at a recent comic sale).
And being able to strip Superman naked has already led to countless minutes of way-too-funny homoeroticism.