RunPee.com would have helped me out when I watched the third Lord of the Rings movie, which seems to have five different endings, at least when you desperately need to use the restroom.
Yahoo! News reports the benefits of RunPee.com:
The site provides recommended opportunities to race to the restroom. It tells you when the action or romance wanes, and gives you a cue (“Baby O.J. is taken from Bruno”) for your exit.
In most cases, I’d suggest not drinking significant amounts of water pr soda before or during a film, but long movies like Harry Potter can’t be watched without minimal hydration of some sort.
God willing, the website will prevent bladder infections and increase the movie theater experience.