Plugin: Create an advanced Plugin example that contains a configuration entity

I'm considering implementing this as I work on my plugin chapter of my book. I was thinking about doing a custom field type as they can have config.

One idea is to create a custom field type for a recipe content type that might have a quantity, unit of measure and ingredient name. It could be potentially be smart enough to use a taxonomy for the unit of measure.Maybe a simpler option would make more sense. Anyone suggestions?