What I really want in an encryption tool is something that I can throw on a thumb drive (portable), lets me encrypt a single file, which I can then decrypt when

What I really want in an encryption tool is something that I can throw on a thumb drive (portable), lets me encrypt a single file, which I can then decrypt when I get to another machine (windows mac or linux) with nothing more than a password. without having to install any additional software/drivers on that new machine, and without needing admin rights. I'd happily keep binaries for each OS on the drive as long as any one of them could decrypt the same file. I'm not moving state secrets around, but it'd be nice to have certain files I carry with me protected in case I lose the drive, but still have them easily accessible on whatever machine I'm sitting in front of.