The Walking Dead Season 1 and 400 Days saves will all carry over to Season 2
Saved games from both The Walking Dead Season 1 and the upcoming 400 Days DLC will carry over to Season 2 of Telltale's episodic adventure. We knew for a while now that Telltale was working on a way to do such a thing, but it seems they have figured it out. Telltale confirmed to GameZone that not only will your decisions from Season 1 carry over, but also the choices you make in the 400 Days DLC which will release later this year.
At E3, we got a brief look at one of the five stories that will make up the 400 Days DLC. We were told that the events in the upcoming add-on will bridge the gap between Season 1 and Season 2 of the game, but that 400 Days will also take place both during and after the events of the first season. Because of that, some of your decisions that you made in the first season could impact and carry over to the DLC. Furthermore, your decisions in the DLC will affect how things unfold in the yet-to-be-announced Season 2.
Should you not have played Season 1 of The Walking Dead, then the decisions will be automatically generated for 400 Days, in the same way each episode of the first season generated your decisions if you skipped one. In similar fashion, if you skip out on the DLC, then your decisions will also be auto-generated for Season 2.
So to sum it all up, Season 1 will affect 400 Days, and 400 Days will affect Season 2. If you miss out on anything, your decisions will be automatically generated. Simple enough?