I was mildly surprised that SparkFun doesn’t carry this. I had to search quite far for it myself. Copper conductive tape. I searched pretty much all over town, couldn’t find it in any of the hardware or electronics stores. Eventually found it for pretty cheap on a site that sells - get this - equipment to repair guitars. All it is, is an adhesive strip of copper that can conduct a signal. It seems like a reasonable thing for SparkFun to carry, I’m using it for a custom step controller: two strips of conductive tape on the controller board, one on an old shoe, step on the board and it shorts. I’m making a 4x4 pad that can be plugged into a computer for gaming use. This project in particular is low on electrical design (I’m just hotwiring a USB keypad) but I can see the tape having other uses, too. Just throwing the suggestion out there.
Sometimes you can find adhesive copper foil in hardware stores near the roof/gutter supplies. Sometimes you can find conductive tape used for burglar alarms (window-break tape).
(no opinion on whether SF should carry it, just throwing out other places you can sometimes get it)
The place where I found it was much cheaper ($2.25 for a 180" long, 1/4" wide roll). I just suggested it because it seems like something a tech hacker could really use. I dunno, wouldn’t it be cool to have a desktop PC that you add, maybe, an extra hard drive by simply PLACING THE NEW DRIVE ON TOP OF THE TOWER?!