Dummy Files

I'm making a selfbooting image of DreamZZT, to teach myself how to make selfboots, and I'm wondering how to put a dummy file in and how to know how large of one. If anyone could help me, that'd be great, because I'd like to maximise my filesize instead of using the pre-made ones I have. Thank you.
To create the dummy file there are a lot of programs in websites like www.dcemulation.com

Just remember this formula to calculate the size in MB

= (capacity of cdr) - (first session) - (program data session)

remember that 1 sec audio is equal to aprox. 8,75MB for the firt session

the name should be 0000.dat or 000.000 or 000dummy.000, you get the idea (make it the first file of the whole dir, and place it in the root dir)

I know there is at least another way to fix the file system (I don't know if it involves the addition of dummy files); but I don't know much about it, so maybe someone else can explain this.