Magical touchstones

[Whitewings]

The idea is simple: magic is the manipulation of certain energies which do not respond to conventional technologies. It is a learned ability and takes time and effort to master, and not everyone can do it. Most people don't have enough potential to be worth developing past the equivalent of first aid or simple arithmetic.

The main purpose of this post is to discuss and develop another aspect of the system: touchstones. Every magician requires them. What I'm looking for are suggestions for what touchstones are, and how that might influence the development of magic.