Musar zu Bereschit 42:19

ארץ אשר לא במסכנות תאכל בה לחם . We have an allusion here to the advice of our sages not to eat like a glutton, but to eat in order to stay alive. We learned this first when the Torah describes the amount that Joseph sold to the brothers. The amount is described as שבר רעבון, i.e. enough grain to still the hunger (Genesis 42,19). This is the meaning of the words לא במסכנות. On the one hand one must be careful not to suffer from under-nourishment; on the other hand one must not eat as a matter of indulgence. This is why the Torah demands that we bless the Lord as soon as we have eaten enough to feel sated, (8,10). We should train ourselves to be satisfied with what G–d has granted us.

ויכלכל יוסף ... לחם לפי הטף . Rashi (47,12) says that Joseph provided based on need. He did not provide luxuries. We must not seek luxuries in our lives. Jacob too said to the brothers: לכו שברו רעבון בתיכם, מעט אוכל "Go back, buy us a little food." We should eat only to still our hunger and not to fill our bellies (43,2).