Is donating winter clothes after their season ends and buying new ones every winter considered extravagance, and is there a more righteous action than that?

There is no harm in giving clothes in charity every year and buying new ones or selling them and donating their price. This does not fall under extravagance if Allah has blessed a person with abundant wealth; rather, it is a good and praiseworthy act. Extravagance is spending in an undue manner or in disobedience to Allah. The righteous predecessors of this Ummah used to give their fine clothes in charity when summer arrived. This act is commendable if one accustoms oneself to shortening one's hopes in this worldly life.