Which external optical drive do you own/recommend for the Retina MBP? Other than the Apple SuperDrive, many seem to require two USB connections to function which is not practical since there are only two USB ports on the device.
Does not need to be fancy if you only use it once in a while. I spent $37 on an earlier model of this Samsung external, right after the new MBP came out. Have had no problems...
Most are bus powered these days; just make sure you get ones that use one USB port. The ones that use two ports won't work anyways because odds are the cables won't reach to both sides of the Mac at the same time.