Core FTP saves its configuration in a file called coreftp.cfg within its directory when used with the -flash flag, keeping your settings truly mobile. Free FTP client, secure file transfer software

Even in its portable form, Core FTP LE offers a comprehensive suite of tools typically found in premium software:

After running Core FTP from your USB drive, use the function in the Site Manager to load those profiles.

While there isn't always a separate "portable-only" installer, the official Core FTP Download Page provides the base software that you can easily convert into a portable version.