How can I run some init code & save data globally for a module?

[TimPietrusky]

In the guide to create a 2D module it would be nice if we could also talk about how to save data globally in the module scope and also init the module once.

[2xAA]

Maybe an advanced guide would be a good idea?
One for quick start/quick reference and another for in-depth discussion on Module specifics.

[TimPietrusky]

I would extend the current guide and add the missing pieces, because then we could use the example module and just extend it with the concepts that are currently missing.