BAS is an eating allowance FOR YOU not your family! It is to pay for meals/food not provided for you by the military. It doesn't matter if you are married or single.
During Basic your meals are provided for you every day so you will not get BAS at all. During AIT you use the Mess, every time you use it the amount gets deducted from the BAS. They are not going to give you meals and then give you money to buy food.