How exactly can one create a good old ISO image using readily available Mac tools? After all, the Disk Utility seems to heavily favor the DMG format. Here is the magic, using the terminal run:

hdiutil makehybrid -iso -joliet -o <output file> <folder with files>/

Note that the files to populate the ISO with need to be in a folder. hdiutil will process the folder contents, not the folder itself. Also note that the trailing slash behind the folder name is a requirement.