Leo says that a bootable backup is a good idea and almost every hard drive comes with disk cloning software in order to make an exact copy of the hard drive he would have. It'll even be bootable. The Chatroom recommends NeoSmart's EasyBCD. Seagate has one called DiscWizard. It's a free download that will clone his Seagate hard drive. Acronis TrueImage is another good option.
On the Mac side, Howard should look at Super Duper. He'll want to make sure the BIOS is set to let him boot from an external drive, though. It also has to be UEFI and he may have to turn off secure boot and boot into Legacy Mode. The chatroom says that Windows won't load from an external drive, but Leo doesn't think that's true. If he turns off secure boot, then it will.
Other imaging options include: