Here is a complete list of RefTeX's configuration variables. All
variables have customize support, so if you are not familiar with Emacs
Lisp (and even if you are) you might find it more comfortable to use
customize to look at and change these variables. M-x
reftex-customize will get you there.
In case you don't use the
customize interface, here's a caveat:
Changing (mostly parsing-related) options might require a call to
reftex-compile-variables in order to become effective.