If you need to make a copy of a key in Davis, ACE Hardware is the place to do it. The key and lock section is on Aisle 14 of the hardware store, which is between 3rd Street and 4th Street. CVS also makes keys.
If you're affiliated with UC Davis, you might be issued a key or two for various buildings and rooms on campus. There is no one master key for the entire campus. For one thing, most of the campus uses Medeco cylinders, yet the dorms use Schlage cylinders. Something like a master key does exist, however. It's a gigantic keychain of master keys, four for the four Medeco lock systems on campus and a bunch of other keys for a few other things. They're stored at a central facility in a series of individually-assigned lockboxes which are checked at the end of the day. They aren't allowed off campus, period.