depends on what it is.. if it's from a scholarship, then no, but you may have to do them a favor later on in life (work for 2 years in a 'at risk' school district, etc)
if it's a grant/loan, then yes, you have to pay it back
you are supposed to use it for school, but technically it can be spend on food, groceries, rent, or whatever else you NEED.. i wouldn't spend it on a vacation or anything..