We take a lot of pills and we do a lot of repairs that involve a lot of tiny screws, so I've been working on tiny nesting cups. After numerous iterations, this is what I consider to be good enough for public use. They're stack-able, the base is thick enough to embed a magnet in, the inner sides are contoured for grip. 

To add a magnet, add a negative part to it - a cylinder in the center bottom, the same size as your magnet. (plus a tiny bit for shrinkage as needed)