The motivation for this project came when I combined my Raspberry Pi voice-controlled electrical outlets with a RetroPie. Due to the number of peripherals and cables involved (a powered USB hub, microphone, two USB controllers, breadboard, wireless remote, plus the normal HDMI and power cables for the Pi), this led to a pretty tangled mess of wires that didn't exactly look great sitting in the TV cabinet. So, I wanted to build a nice case to hold everything that looked something like a regular game console - ideally with external connections for the USB devices, an HDMI port, a power switch, and a single power cord (shared by the Pi and the USB hub).
The normal way to do this would be with a custom project box and regular panel mount connectors, like these HDMI and USB ones from Adafruit. To do that, you need to either machine or laser-cut a custom panel to fit all the connectors, and I don't have the means to do so (yet....cough, cough, Full Spectrum Laser contest). I've seen a bunch of cool Raspberry Pi LEGO cases out there - but most of them just enclose the Raspberry Pi itself, without all the extra space for a USB hub and breadboard, or sturdy external panel mount connectors.
Enter Sugru, a self-setting rubber that you can mold by hand, kind of like Play-Doh or modeling clay*. Let it sit for 24 hours and it hardens into a tough, slightly flexible rubber. I'd recently used it for the first time to waterproof a small DC motor for a different project, and realized it would be great for this: build a case out of LEGOs, and use Sugru to firmly seal in the panel mount connections - no machining or lasering required. Rather than using regular panel mount connectors (which have screw terminals that I wouldn't need for this approach), I could use either very short extension cables or female-female couplers to create the panel mounts. The result is a very fun and kid-friendly approach to building a stylish case, without requiring any tools.
So, you could use this idea for ANY project that requires panel mount connections - it doesn't have to be Raspberry Pi-related. I'll just be using my RetroPie "console" as an example since it contains a variety of different connectors (HDMI, USB, barrel jack). I'll also include a power switch (a nice addition since the Pi doesn't have one built in), but that part requires a bit of soldering. It should be pretty easy to adapt the process for any other connections you need for your project (VGA, RCA, pushbuttons, slide switches, etc etc).
*Sugru has an Instructables account where they post their own projects that use Sugru. I am in no way affiliated with the company, nor is this an endorsement of the product. I first found out about Sugru when I won a couple packets as a prize in a different contest, and decided this would be a cool use for it. If you know of a different, cheaper, or better material to use, please mention it in the comments below (for example, I'm curious if plain old modeling clay would work, but my hunch is that it would be too brittle once dried).