My Dear Friend,
Vat & Service Tax is applied both or not this is vary from case to case.
for better understanding i am giving you a live example:-
Haldiram:- they just provide food & other items of eatable. But there always self service means they not provide any other service so they just charge VAT in his bill amount not service tax.
Pizza hut :- they provide table service also with fooding so they sharge service tax as well as VAT.
If you are provide just cataring services then VAT is not liable there beacuse it is covered specially by service tax