Dropbox works for me in that regards pretty well. I have my own structure of folders with my personal documents (as well as tons of local and general survival information and eBooks) in PDF, Word, and surely as plain images. I'm keeping them in most common formats, so not to be dependent on any special software in order to view them or print them out. However most sensitive documents (credit cards, ID's, ssns, grand deed) are in a separate folder above the Dropbox structure (so not to expose them during transferring or on the cloud). But still, they are without any special protection. I never part with my phone, and when on the streets I have its lock screen password protection invoked automatically (when leaving the range of home or work wifi hotspot). Still, it is possible to reach them, as they are actually on the removable T-flash card. But that's also important, as if the phone dies (drowned for example) - I can still get my information out and intact.

Also I'm using the aWallet app to store my online passwords, and the Emma Personal Wiki app to gradually build my own knowledge base of local survival information in particular. It's also auto-synchronizing through the Dropbox with other Androids and PCs as well, and supports HTML sytax, so you can build quite complex data sets with it if necessary. This is the only wiki, natively supporting truly functional check boxes in the text - great for making check lists, obviously.

The later could be replaced with a more convenient Evernote app, but I was not able to justify their subscription fee model, nor their proprietary notes format. But that's definitely the best option for those not familiar with Wiki editing or HTML.

In the recent time I've started to take my notes with the Samsung Note 3 pen, using the dedicated Samsung S Note app - very natural way! Also you can add external images to your notes. But still figuring the best way of making them synchronized with Dropbox automatically (plan to write an app for that).

Almost forgot! The fantastic scanner app I'm using - the CamScanner. It creates perfect scans of documents using the phone camera. I have all of my equipment user manuals scanned with it in no time (tried a dozen of similar apps prior to that - you can trust me, this one is the best).