וַיִּקְבֹּ֞ץ אֶת־כָּל־אֹ֣כֶל ׀ שֶׁ֣בַע שָׁנִ֗ים אֲשֶׁ֤ר הָיוּ֙ בְּאֶ֣רֶץ מִצְרַ֔יִם וַיִּתֶּן־אֹ֖כֶל בֶּעָרִ֑ים אֹ֧כֶל שְׂדֵה־הָעִ֛יר אֲשֶׁ֥ר סְבִיבֹתֶ֖יהָ נָתַ֥ן בְּתוֹכָֽהּ׃
און ער האָט אױפֿגעזאַמלט די גאַנצע שפּײַז פֿון די זיבן יאָר װאָס זײַנען געװען אין לאַנד מִצרַיִם, און האָט אַרײַנגעטאָן די שפּײַז אין די שטעט; די שפּײַז פֿון די פֿעלדער פֿון אַ שטאָט װאָס אַרום איר,
Tze'enah Ure'enah
“The grain of the field around it” [41:48]. They took earth from the field and mixed the earth with the grain and the grain did not spoil.33Rashi, Genesis, 41:48.
Rashi
אכל שדה העיר אשר סביבתיה נתן בתוכה THE FOOD OF THE FIELD WHICH WAS ROUND ABOUT EVERY CITY LAID HE UP IN THE SAME — for every district preserves its own produce; and for this people always put amongst the grain some of the earth of the place in which it grows and this prevents it decaying (Genesis Rabbah 90:5).
Chizkuni
אוכל שדה העיר, “he stored inside each city the kind of food had had grown in the vicinity of that city.” By doing this it would be near at hand when the time came for drawing on these supplies.