A seamless texture done with circuitboard bits and pieces, along with some batteries (probably not recommended).
Mostly for creating clutter in models etc.
Basic process:
Make pieces, make phys, duplicate a bunch, shove them all into a box, have a ortho camera above and create a 2048x2048 image; You have a base. Render isolated versions of your pieces, Open in photoshop, offset your image by 1024x1024, cover seam in random bits and pieces, give drop shadow or something so it looks good.
Done.
Were I wanting to improve this, I'd include some stray wires, little half-complete circuit boards - but it serves its purpose right this second and can always be added to in the future, although I'd probably try make it into a substance designer material next.
The most fun part.