What role do religious rituals play in religious identity? Are those who are observant 'more religious'?

I am a religious studies student and have been focusing my studies on Judaism.  My thesis is on the role food plays in the daily practice of the Jewish faith, as well as during religious holidays.  As I have been researching, some questions continue to plague me, and so I am submitting them here for discussion.  What does it mean to be Jewish?  Christian?  Muslim? What are the minimum boundaries; meaning can you be Jewish without keeping Kosher? without celebrating holidays?  Are observant Jews "more Jewish"?  If you don't take communion are you "less Catholic"?  If you don't fast during Ramadhan are you "less Muslim"?  How do we define ourselves through our religious beliefs and what role do our rituals play in that definition?  Finally, why does food play such an important role in religious rituals, particularly those in Judaism?  I would be interested in hearing what everyone has to say!