Essentially, don't put it on the web, don't email it, and don't even SMS it. What's left? We still need to talk to each other, and in modern times, that means digitally.
The Content Addressable Graph (BaseParadigm) is an answer.
The graph is a super-schema: a uniform way to represent many (arguably, all) kinds of information. Unlike other formats, the Content Addressable Graph has identifiers baked in at every level, enabling documents to be broken into pieces while remaining linked together.
In a Content Addressable Graph, no single application need keep track of a definitive version of the data. Updates can happen between peers as needed. A contact management application and a calendaring application can both act on the same data without needing a third service to help them communicate.
This unique property of the Content Addressable Graph changes everything. Now that no third service is needed, data for all applications can be communicated using local networking like Bluetooth, stored on any storage device like SD cards, and accumulated and backed up as desired in an 'offline' fashion.
To keep things available across devices, generic servers can still be employed to store all data. Such servers would not discriminate between applications. Social and financial data end up in the same place. However, because applications are independent, a server isn't even needed.
I'm diligently working on BaseParadigm. If you are interested in using it, learning more, or helping with the development effort in any way, please contact me.