A 10x, 14x and 20x magnfier.
The are on a key ring. The 20x is a tiny thing.
http://www.opticsplanet.net/bausch-lomb-triplet-magnifiers.html
I also carry a Chelsey colour filter for testing gem colours, and a dichroiscope, they are small too.

(I spend about an hour a week on average looking at junk jewelry in thrift stores)
_________________________
May set off to explore without any sense of direction or how to return.