
My "Emergency" Wallet is password-protected, naturally. Just don't forget this master password, or you're sunk.
In one of the drafts folders of one of my many web-based email accounts, I keep a very useful list of frequent-flyer numbers, login names to various websites, membership numbers, and my husband's pants measurements. Random snippets of helpfulness, but nothing too top-secret. After all, I've only entrusted it to a drafts folder of a webmail account, not exactly Fort Knox For Data (just ask Sarah Palin). And while this list is easy enough to access on a real live computer, viewing/editing it in the iPhone's browser is a bit of a pain.
Happily, eWallet provides secure, password-protected storage right on your iPhone, for whatever info you can throw at it. You can organize your info into wallets (say, Personal, Family, and Emergency), and then categories, and finally onto individual cards. eWallet has card templates for things like your contact lens prescription, credit-card info, insurance policies, emergency numbers, settings for your router, software serial numbers, and a whole bunch more.

These Emergency wallet categories contain individual cards. You can set up as many wallets, categories, and cards as you like.
The app is easy to set up and use, and 256-bit AES encryption keeps your information safe. Don't forget the password you put on your Wallet, though--the app can give you a hint, but if you really do forget, there's no way back in.
If you use a Windows PC, you can sync your iPhone's copy of eWallet with a PC version of eWallet. But currently, Mac users can't get eWallet's info out of their iPhones. There's no way to import info from Macs either: The only way to get info in is to type it on the iPhone's keyboard, and the only way to get it out is to... read it. You know, with your eyes.

On the front of a banking-info card, you can change up the colors used, if you're still up for tweaking after you've typed in all that info. Tapping the letter "i" in the lower-right takes you to...

...The back of the banking card, where you can add more info.