Doing builds of a certain mobile-operating-system-based-on-Linux usually doesn't work on my tiny laptop due to the small internal ssd size, but keeping a source tree on an external disk works really well.
Thankfully we are finally seeing external drives that support the "stream" USB storage specification. Unfortunately, you can't seem to find them in the "pre-packaged" form, so you have to build your own.
This is the device I've been using for a few months now, with great success. It's fast, portable, and seems durable so far. Throw a fast SSD into it and you have a solution that is cheaper, and faster, than a pre-packaged drive. I've been using Samsung 850 EVO drives a bunch, they work well, and easily hit USB 3.0 line speeds.
Another enclosure I got can be found here: http://www.amazon.com/Inateck-Tool-Free-Enclosure-UASP/dp/B00FCLG65U
it runs at the same speed of the StarTech one, but the cable isn't built-in, so I have one less thing to loose when I travel.
If you search for others, the magic string to look for is "UASP", and make sure you have the 'uas.ko' kernel driver enabled in your build (you do run a custom kernel, right?) so that it can actually go as fast as the hardware will let it.
Although, my laptop is getting old, and 8Gb of RAM is almost impossible to build large systems with these days, so maybe I just need to get a new laptop, anything anyone would recommend with lots of ram, high-res screen, and Intel graphics?