If you burn with Nero, -everyone has Nero, do they not?- you just keep adding files/songs until the CD is full and the bar at the bottom changes colour.
If you are making a CD of MP3s, for the car, for instance, you can get more on, depending on the quality of the MP3, lots more. Again with Nero, it may be impossible to fill up the CD with MP3s unless you specify that they are data, not music. This may have something to do with the number of titles/file names. They still play.
It isn't a bad idea to have copies in the car. Several members here have had CDs stolen from their car.
If you put the files, MP3 or WAV, in a folder on the computer and then switch the computer off, they will go into alphabetical title order, which I think is something to be sought after.
That's what happens on mine, anyway.