What are your theories so far?

Spoilers of course!

Here are the mysteries so far: Who Killed Cal? // Who stole the tablet? // What documents are inside the tablet? // What do the numbers on the cigarette mean? // Why does Xavier hate Cal? // What happened to Xavier’s wife? // What was the cause of the apocalypse, what exactly happened on that day?

Apocalypse: my guess is that a huge asteroid hit Earth and caused a huge tsunami. People on Earth are all dead, except for the people that were inside the bunker when that happened.