If you switch to your "civilian" outfit while in a store, it will highlight all non-civilian equipment (such as (most) armour and weapons) in purple.

[![Civilian and non-civilian trade goods](https://i.stack.imgur.com/6KDEr.png)](https://i.stack.imgur.com/6KDEr.png)

Grain, meat, grapes etc. count as civilian items, but not butter. Why is this, and does it have any effect on gameplay?