Rashi on Exodus 12:39/רש"י על שמות י״ב:ל״ט

1עגת מצות means a cake of (made of) unleavened dough (Mekhilta); dough which has not become leavened is termed מצה.

2וגם צדה לא עשו להם NEITHER HAD THEY MADE FOR THEMSELVES ANY PROVISION for the journey. This is stated to tell how praiseworthy Israel was: that they did not say, “How can we go forth into the wilderness without provisions?” But they had faith and set forth. This it is that is referred to more explicitly in the prophets: (Jeremiah 2:1) “I remember for thee the affection of thy youth, the love of thine espousals, how thou wentest after me in the wilderness in a land that was not sown”. What reward is afterwards set forth there? “Israel is the Lord’s hallowed portion etc.” (Mekhilta).