Jamieson, Fausset and Brown on Genesis 27:28

Ge 27:28-46. The Blessing.

28. God give thee of the dew of heaven--To an Oriental mind, this phraseology implied the highest flow of prosperity. The copious fall of dew is indispensable to the fruitfulness of lands, which would be otherwise arid and sterile through the violent heat; and it abounds most in hilly regions, such as Canaan, hence called the "fat land" (Ne 9:25, 35).

plenty of corn and wine--Palestine was famous for vineyards, and it produced varieties of corn, namely, wheat, barley, oats, and rye.