Supergirl has always been good at cliffhangers, even on an episode to episode basis, so it's no surprise that the Season 1 finale ended on a big one. Who's in the pod on Supergirl ? At the end of the episode, a Kryptonian pod just like the ones that took Kal-El and Kara Zor-El to Earth crash landed on Earth. If Supergirl returns for Season 2, there's going to be a new alien visitor.
When Kara cracked open the hatch, she gasped "oh, my God" — so I think it's safe to say that this is a face Kara recognizes. In an interview with Entertainment Weekly, executive producer Andrew Kreisberg teased that that in the pod is "...an important character, and they’ll play an important role in season 2." He also says that this will shake things up and excite fans. My guess is that it's her parents, or at least her mother Alura. Am I mostly just saying this because I want more Laura Benanti on Supergirl? Of course, but that's not the point. In DC comics, Supergirl's family and all of Argo City on Krypton survived their planet's destruction.
Other than that, I suppose the pod could hold another Earth's doppleganger, a clone, or an android version of Kara Danvers or Clark Kent. There is a version of the character Superboy in DC comics that is a clone of Clark, and he is also connected to Project Cadmus. I doubt that Supergirl would go for a villainous character as big as General Zod. I haven't even considered the possibility that the pod could be un-manned, or un-aliened or whatever. Maybe it contains a "what" instead of a "who;" that's even more mysterious. Non and Indigo may be defeated on Supergirl, but Kara's journey as a superhero is only beginning.
Image: Cliff Lipson/CBS