Starting today, Facebook is rolling out a new Trusted Contacts feature under your account security settings. Here, you can pick three to five folks who will have the power to help you when you lock yourself out of your account.
It's pretty unlikely that you'll get accidentally locked out of your account such that you're helpless to get yourself back in, but it's not inconceivable. When it happens, give one of your trusted buddies a holler, and they'll be able to get a code and instructions to get you access.
As the post from Facebook's security team notes, you should only pick people you would trust with a key to your house, because you're handing them a lot of power. Trust is a hard thing, but it will be worth it when you're in a bind. [Facebook]