If you're concerned about your data's safety, consider using Anchorfree's Hotspot Shield free VPN service. Hotspot Shield has been a great way to lock down your laptop's wifi for a long time now, and just recently they have released instructions on how to take advantage of their service on an iPhone / iPod touch. Pleasantly, the service does not require that a program be downloaded to your device, but rather takes advantage of the iPhone and iPod touch's built-in VPN functionality.
My only gripe with Hotspot Shield is that it can sometimes be challenging to get the VPN to successfully connect. Anchorfree recommends performing a quick reboot of your device to get your connection going, but in my experience even that can be a hit-or-miss scenario. But it's still better than letting that creepy guy that keeps hitting on the barista peruse my http requests. 'Cause I'm not paranoid, but I'm sure that's what he's doing.