The best thing to do is organize your files so that you have one directory that contains DATA. Not programs, games or anything else!
When you put all of your data files, such as word docs, excel spread sheets, pictures, etc., You would in 99.9% of the time be able to backup this directory onto a single DVD. If your backing up music, well you'll have to make sure it setup on a sub-directory called music and just back that up.
Since your have all your other install disk, for the various progams you use, you don't really need to back them up. You can always install them again..
I've been backing up severs and LANS using this model!