I have a 15" Retina MBP.. 512 gig hard drive. And I am out of space. I previously had the older MacBook Pro and used the SD card slot to expand my storage. Mainly only used that portion for my iTunes music etc. But now. I partially think I have a system error, which at 1 minute I have 150 gigs free and 5 minutes later I'm getting a pop up that says my storage is almost full. Thats a topic for another day. I'm wondering what are you all using to expand your storage. Are you all using a simple uninvasive USB-C Flash drive.. Are you all going with cloud services?