Or HaChaim on Genesis 42:5/אור החיים על בראשית מ״ב:ה׳

1 ויבאו בני ישראל…כי היה רעב, The children of Israel arrived…for there was a famine in the land of Canaan. The fact that there was a famine had to be repeated. This is to explain why the Torah first wrote בתוך הבאים. You should not ask where these הבאים have been mentioned previously so that the Torah could describe the brothers as "being amongst them." Once we are told that there was a famine in Canaan it becomes obvious that many other people from Canaan must have been going to Egypt to buy grain there.

2The Torah also wanted to indicate that the brothers devised a clever scheme to disguise themselves "among the other travellers." They created the impression that they were in Egypt for the same purpose as all the other travellers from Canaan, whereas in reality they were searching for Joseph. In other words: the brothers' disguise was to appear as shoppers for grain. This ought to have been an easy way to camouflage their real purpose because of the famine in the land of Canaan.