LiveJOSM is Debian operating system with preinstalled JOSM and some useful JOSM plugins that can boot without installation to a hard drive. LiveJOSM is based on DebianLive.
There are some ready to download images:
Note: Username and password is: user / live.
Note: UEFI Secure Boot is under development. It has to be switched off for now to boot successfully.
There is a documentation on How do I write a CD/DVD/BD image to a USB flash drive.