I gotta second this. My dad and brother came to help me run water and wiring to my new detached garage. My dad insisted we through in extra cat5 and we ended up using it to run low-voltage switches so we can turn on and off the garage lights from the house. Also, there's strands left for phone if we need it. The tubing for the water was easy and we installed a yard hydrant, which was simple as well, so I now have water just outside the building. We're actually now working on a plan to bring in a line through the wall that I can hook to the yard hydrant when I need it that will feed a utility sink just on the other side of the wall.
Running extra stuff is cheap and worth it in the long run.