Meet the USBdriveby: a wearable device that allows you to install a backdoor and override DNS settings on any unlocked machine. It achieves this by emulating a keyboard and mouse. You can disconnect it when done and still have control over that machine and its network traffic. The device is programmed to evade security measures in OS X.
In the above video, Samy Kamkar explains how this all works. How would you go about making your own USBdriveby? For starters, there is some code for you to study on GitHub. As far as the hardware goes, you will need a Teensy 3.1, which costs only $20+. You also need a chain to wear your USBdriveby around your neck. The good news is Samy has made a lot of useful info about this project available online.