To burn to a recordable CD so you can burn to it again:
In Disk Utility, create a disk image that contains the files you want to burn to the disc.
The files must be from a partition with a Mac OS Extended disk format. To check a partitions format, select the disk in Disk Utility, and look at the information at the bottom of the Disk Utility window.
Select the disk image in the list at the left, and then choose Images > Burn.
Select the Leave disc appendable checkbox. If you dont see this option, click the triangle in the upper-right corner.
Insert a blank recordable CD in the optical drive and click Burn.
To add more files to the disc later, follow the steps above. You can continue this process until all available space on the disc is used.