Your USB drive should be able to store and boot as many operating systems as its storage capacity allows.
Rufus is an open-source program that creates bootable USB sticks for Windows installation and more. Compared to Microsoft’s Media Creation Tool, Rufus offers many more options for configuration setup.
I read about DasBoot on Infinite Loop. It's a freeware app that purports to make USB flash drives as well as USB/Firewire external hard drives Mac bootable, for the purposes of using them as Mac ...