What data is stored on the iPhone or iPad (or iPod touch)?

Only those items that you choose! With ForeFlight Mobile, you can choose what items you want and for what geographic areas you want those items. 

To set up what is stored on your devices, go to the 'More' page and tap on 'Downloads'. Select your 'Required Downloads'. Also, tap on a coverage area under 'Download Settings' to select downloads for Taxi Diagrams and A/FD, Terminal Procedures, VFR Charts, IFR Low Charts, IFR High Charts, IFR Planning / Ocean Charts, Helicopter Charts, and High Resolution Terrain. 

To learn more, please read about Downloads in our Pilot's Guide.