It is my understanding that some of the old PPC systems are able to boot from USB, but I do not know which ones or how it is done. I don't believe it is straight forward since I think it involves issue commands to the Open Firmware. If you search the PPC forum, you may find a few posts about it. If not there, then a general Internet search will give you some information about booting from USB on those PPC Macs.
As far as making a bootable CD, I'm not sure how that would be accomplished. It would be easier to make a bootable Firewire hard drive since all you would need to do is make sure the System folder is blessed (has a happy Mac icon on the System folder). There was a simple trick to do that back in the day, but I don't recall specifics or if it can be done on a non-OS9 system (probably can be achieved with the 'bless' command, but only macOS 10.14 --perhaps 10.15-- or earlier can read the older HFS formatted disks).