Today, for you:
Wasteland 2 will be free at GOG until December 13th till 2PM UTC. All you need to do is log into your GOG account, find the Wasteland 2 giveaway banner on the main page (it's a little ways down) and click the green button. Done. Game will show up in your library shortly.
Extras includes a manual, map, wallpapers, reference card, a concept art book, and the soundtrack. Also, you get both the original version of the game and the Director's Cut, and you can also get a code for a free copy of the first Wasteland. To find that code, go to your GOG library, click on the game, click "More", then select "Serial Keys". Copy paste the link and the rest is easy.
Have a look if interested and enjoy.