I use Cryptainer portably (love it) and on my USB stick's root drive, have a 2Gb encrypted volume that has no file extension. I don't know how that works, but it does. This volume contains all my project work, plus my password safe.
I also just switched to use PortableApps Backup to back up my USB stick. I discovered this morning, to my horror, that it does not copy this project file. Everything else is there except this one. I just assumed it would copy everything on my stick. Does it need a file extension to back up those bytes? If so, why? I know I can do a straight drag-and-drop to copy the file, but would it be possible for Backup to handle it routinely?
(This is a problem for me. I left my USB stick at home and needed this project volume to continue my work and to access my passwords. My commute is an hour long and I carpool, so I can't just go get it... which is one reason why I back up my stick so regularly, expecting to be able to continue working if I forget that little thing or somehow lose it, or it wears out.)