Just realized this feature yesterday:
https://www.arduino.cc/en/Guide/PortableIDE
You can pack the entire arduino and all its libraries, core files, board files, sketchbook folder etc. into one flash drive and run off the drive.
This is very good news for workshop organizers and instructors/students. I tried it with 1.6.5 and it works. I've used 1.6.5 for a few years and never knew this feature exists. Only works on windows though, still very cool.