I recommend getting separate hotel rooms, unless you want to sleep with your buddy. Is this buddy hot, yet in your league?
I recommend to only drink bottled watter.
Also, go out to the real Mexico, not the sanitized tourist area. Participate in the (if any) city's Christmas parade, and Misa del Gallo. Find out if firecrackers are legal and torch some yourself.
Also, don't go on my advice alone. Get some from individuals who are actually familiar with Mexico.