Out here in the land of the money hungry and over regulation, I was quoted $850 for a 1mil GL to cover catering for a year. Vending, so far I have grabbed at a per event basis @ $90 per event. I did find a policy recently for a cater that covered a 1 time event (banquet hall, food liability, halls commercial prep kitchen, the whole event) for $90 based on 175 attendance. It may be different where your at, but here it seems catering and vending are considered 2 separate liabilities and require different policies.
Dedicated Stick Burner, Pitmaster @ All About The Q, facebook.com/itsallabouttheq KCBS CBJ