How do I determine what xtras are needed?

Question

From the searching I have done it appears that xtras equired are mostly trial-and-error.
Is there an efficient way to determine what xtras are needed for each lindividual movie?
My programs are divided into a series of sequential movies.  At the end of each movie
there is a goto statement to launch the next movie.  Does that require me to determine
xtras for each separate movie? 
In a perfect world there would be a way for Director to search a  folder for and present an aggregate list of all xtras required for that set of movies.
If no such method exists, what is the recommended hunt and peck system?

Answer 1

Thanks for the response, rduane.  But I refer to the procedures as a bit random for the reasons you mentioned in your explanation.  For example, you stated that, "Director will normally add all of the Xtras that you need to each movie as you build it".  And, yes, I know that it does add some automatically.  But, if Director really does "add all of the xtras that you need to each movie as it is built", how could I ever jump to one that is missing a needed xtra?  If it needs it, why wasn't it added when it was built?
So, that's the reason I mentioned "trial and error", and "hunt and peck".  The system is not reliable in its handling of xtras, or which ones are needed where.  I am familiar with workarounds such as going to each movie and selecting Modify>Movies>Xtras to see which ones Director has added,  But that is all it tells you.  It does not tell you if it has added all the xtras "needed".  And when the error message comes up, it does name the missing xtra, but not which movie needs it.  So, one has to go find the named xtra and copy it over to the Xtras folder. 
At least, that's what I do to fix it.  But I asked the question because I wanted to know if Xtras handling itself is unreliable, or if I'm doing something incorrectly.
Dewey-+