Adam Clarke on 1 Samuel 28:24

The woman had a fat calf - The ancients used great despatch in their cookery. In hot countries they could not keep flesh meat by them any length of time; hence they generally kept young animals, such as calves, lambs, and kids, ready for slaughter; and when there was occasion, one of them was killed, and dressed immediately.

Unleavened bread - There was not time to bake leavened bread; that would have taken considerable time, in order that the leaven might leaven the whole lump.