There's no SD card slot in the newor the 12-inch MacBook. I hate this. I really do. I'm transferring files from my camera to my computer all the time. Without this slot, it's incredibly difficult to get my work done.
The Satechi Type-C USB Pass-through Hub is my savior. It can be plugged into your MacBook's USB-C port -- just like you would a thumb drive -- adding two USB 3.0 ports, one SD card slot and one miniSD card slot to the computer. There's also an embedded USB-C slot that lets you charge your computer or other devices, but not transfer data.
One thing, though: The device runs along the side of your MacBook while connected, but only connects through the USB-C port. And since there's nothing other than the lone port to keep it connected, if you attach a large enough device, like an external hard drive and then move the laptop around too much, it can detach quite easily.
Also if you happen to lift the laptop up with the hub plugged in, as well as a few devices plugged into the hub, you risk bending the hub in a way that may make it snap off from the port. So be careful. With the amount of ports it supports already, the lack of an HDMI port is disappointing. But if you can be mindful of its fragility, the convenience it brings, especially if you use a dSLR camera, is totally worth its sub-$40 price.