Financial aid/tuition question ?

My son is going to a college in our home state that has given him his financial aid package and we accepted it. It consists of scholarship, pell grant, grant from actual college and both subsidized and unsubsidized Stafford loans. It totalled $14,050. That is the school's estimate of tuition, including dorm and meal ticket. Their web site also now says the real cost is supposedly actually only $12,900. They do the package to be sure he has enough to attend. So, what happens to that extra $. Can he use it on campus for expenses, such as supplies? Or does the aid office take it back and put it on the Stafford, or what? This is my oldest and first experience with college, etc. We have had so many questions!