I'm trying to find the title and author of a book that was read to me
by an elementary school teacher.  The part that sticks out the most in
my mind involves one of the characters agreeing to die a certain
number of years earlier than he otherwise would have in exchange for
something (no idea what it was...maybe to rescue a friend).  The
agreement was something along the lines of if the kid would have
normally died at 80, he would now, after entering into this agreement,
die at 75, etc.

A majority of the story takes place during the Mexican Day of the Dead
or is at least centered around the upcoming holiday.

I realize that this is an incredibly broad question that may be
unanswerable, but I don't really remember any other details.