Either encrypt the data you carry, or use an encrypting USB key such as IronKey. I keep my passwords in an IronKey, and don't need to worry about stolen data if the key is lost. This is much easier than remembering to encrypt data just for transport on a low cost non-hardware encrypting key-- and on a cheap key, you still need to zero the clear data after transport (you do remember that the deleted files are still there right?).
As for the cloud (dropbox et al), if the data is not encrypted why not just publish the data on your personal website?
I too use a memory stick for a few specific files. I've gotten so many passwords for so many different accounts that I've had to write some of them down in a Word file. My financial institution passwords only go in my head, but plenty of others are in this file.
I don't want them anywhere but with me, so I don't keep the file on my work computer or Dropbox, just on the memory stick in my pocket and on a backup at home. I had a scare the other day when I thought I had lost the drive. Even worse, on that particular day, I had violated my no financial documents rule and put a PDF of an old tax return on it. Bad idea.
I eventually did find the drive, but it highlighted the need for an easy encryption system for the files on that thumb-drive.
Actually I'm still on the look-out for a better way of doing this (synchronizing my email across home and office machines) -- and by "better" I mean something that doesn't require and effort on my part :-)