Rashi on Exodus 16:5/רש"י על שמות ט״ז:ה׳

1והיה משנה AND IT SHALL BE DOUBLE — for today and for tomorrow.

2משנה DOUBLE of what they were accustomed to collect on each day of the other days of the week. I say that the words, אשר יביאו והיה משנה “what they bring shall be double”, imply that after they have brought it home they will find it double in measure of what they had been gathering and measuring each day. This is the force of: “they collected double bread” (v. 22) — when it was collected it was found by them to be double food, and this is the meaning of (v. 29), “therefore he giveth you on the sixth day the bread of two days”: He gives you a blessing — old French foison, — abundance in the house that you may fill the Omer twice, as bread for two days.