How do I become a Hero in die2nite?

You may now purchase days of Hero time on the Die2Nite website.

There's also another way to become a hero: manage to pull out of a town that has lasted for five complete days as the Last Man Standing, and you'll be rewarded not only with a special distinction but also with a certain amount of Hero days depending on how long you survived. You can read up on Last Man Standing and the rewards here.

Now that the game is out of beta, you may buy hero time for roughly 12-15$ a month.