Here's an interesting tip from The Apple Blog about hiding sensitive data in plain sight. In this instance, Dave Greenbaum explains how he uses an app like Apple's Address Book to plainly display a credit card number. The catch is that, upon first glance, the record looks like any other collection of contact info. Only Dave knows how to read the data "hidden" inside.
It's not uncrackable, of course, but still a clever idea. Perhaps you could use it to obscure less sensitive data if you'd rather not do it with a credit card. Alternatively, apps like Knox and 1Password offer true encryption and are relatively inexpensive.
Dave's solution is free and something we hadn't thought of. Head over to read the whole post. Nice thinking, Dave!