Apple Cinema Display 27" with early 2015 MacBook Pro I have a 13" early 2015 MacBook Pro with retina, and i am considering buying a second-hand 27" Apple Cinema Display.

The 27" LED with single cable with three connectors (Mini DisplayPort, MagSafe, and USB 2.0). 

What cables/adapters do I need for this display to be able to use full resolution the screen has to offer?
You won't need any separate cable to connect the display to your 2015 MacBook Pro.

A Mini DisplayPort cable is attached to the display which can be plugged into one of 2 Thunderbolt 2 ports present on the left side of your MacBook Pro (besides MagSafe 2 connector).