Gratitude has two dimensions: the acknowledgement of the other's autonomy in that they didn't have to give the gift; and the appreciation of the value and meaning of the gift so that there is a correspondence established between the valuing of the gift by the recipient which is commensurate with what the grantor of the gift has and had in mind.
The former (recognizing autonomy) refers to the choq, the latter (appreciating the gesture) to the mishpat. It resembles the dual decision-making that goes into every market transaction: (a) do we want to do business with you; and (b) at what price.
Those who belong to the same home need not qualify the choq. They can take without asking so long as they appreciate the mishpat by saying 'It is good.'
The demonstration of an under-appreciation of the value of a gift comes in the form of waste. If you waste what is given to you, you are implicitly not appreciating it. We don't waste food out of respect to God's providence for having granted it to us.