Nobody has mentioned this solution, probably because it's relatively new. A new feature they just released on iTwin lets you use your iTwin device as a key and encrypt files before storing them in Dropbox. You can carry the iTwin with you. (It's a little USB device.) Then use it as a key if you want to retrieve your passport/cc info from Dropbox. Its very safe, since the physical key is required to access your data, in addition to the usual Dropbox password, and the encryption/decryption is done right then and there on your laptop.

I've been using this on my international trips. I actually don't keep any copies of this sensitive info physically on my laptop. So I'm safe against anything that may happen... laptop theft, loss of the iTwin (useless without password), breach of my Dropbox account (useless without iTwin key).