Exodus 16:2

And on that day the bread which they had brought out of Mizraim was finished. And all the sons of Israel grumbled against Mosheh and against Aharon in the desert.

AND THE WHOLE CONGREGATION OF THE CHILDREN OF ISRAEL MURMURED AGAINST MOSES. Scripture should have first narrated the nature of the complaint just as it did in Marah. and Rephidim,. and at all other complaints — and stated here first: “and there was no flesh to eat, nor bread for them to the full, and the people were famished for bread.” Now Rashi explained that the reason Scripture specifically mentions [that the date of their arrival in the wilderness of Sin] was on the fifteenth day of the second month is in order “to make this encampment unique. On that day, there came to an end the provision which the Israelites took along with them from Egypt, and they now needed the manna. It thus informs you that they ate sixty-one meals of the remains of the dough [which they had baked in Egypt on the day of the exodus].” [Thus far the language of Rashi.] This is a tradition received by our Rabbis, and the reason that Scripture did not [first] explain the nature of their complaint was that it had not elaborated on this miracle which was done for them secretively, [i.e., that the remains of the dough furnished sixty-one meals]. And it is as I have already written in Seder Vayigash concerning the reason [that Scripture is disposed to be silent on hidden miracles].
Rabbi Abraham ibn Ezra wrote that Scripture records the date on the fifteenth day of the second month in order to explain that a month’s time had already elapsed since their departure from Egypt. In the meantime, they consumed the bread they took out of Egypt as well as their cattle, since they were a great multitude of people. This was the reason for the murmuring.
In my opinion, the reason for their complaint is to be found in the Scriptural expression, and they came… unto the wilderness of Sin. When they came to that wilderness far away from Egypt, they began saying: “What shall we eat? What will this great wilderness into which we have come supply us with?” It may be that at first they had thought that after a few days they would come to the cities round about them. Now that a month had gone by and they found no city of habitation, they said, “We will all die in the great wilderness into which we have come.” This then is the meaning of the verse, And the whole congregation of the children of Israel murmured against Moses and against Aaron in the wilderness, the murmuring being because of the wilderness. And so likewise the people said, for ye have brought us forth into this wilderness, to put to death this whole assembly by famine. Thus they mentioned “the wilderness’ and “the assembly,” therein stating that a large assembly such as this will undoubtedly die of hunger in this great wilderness. The Holy One, blessed be He, hearkened unto them, and He now began to prepare a table for them in the wilderness until they came to a land inhabited.