You can set up a recordable CD (such as a CD-R or CD-RW) to accept more disk images after it is initially burned. This way, you can burn a disk image now and add to the disc later until there is no more room on the disc. This is called “multisession” burning.

To how to record to a disc more than once, open Disk Utility, in the Utilities folder in the Applications folder, choose Help > Disk Utility Help, and search for “multisession burning.”