daisy chaining includes

I'm trying to clean up about 2000 lines of whacked out newbie code i've created. Is there a way to daisy chain includes? I have about five includes in each header and I was thinking of making one include file and linking to that. And furthermore :} is there a way to include within a function if i do make several include files? So the file is only called when the function is? Would this be a good way to cut down on server processes? Or would it offset by the disk-to-parsed time? I had a db_queries include but i've dropped that so that I can use one variable and unset it each time. This is a way to save memory right? Dumb question I think. Thanks, John