Just off the top of my head, you need to:
Identify the various venues you wish to vend at. Make a note of the municipality they're located in. Contact Dept. of Health and inquire about permits, inspections, etc.
Contact the various venues and inquire if BBQ vending is something they'd be interested in. If so, how much would it cost you?
Contact your insurance agent and get a quote on a product liability policy.
Contact an attorney and an accountant. You'll need to set up a business entity. Don't forget, Uncle Sam will want a piece of the action.
Once you gather all your facts and figures relative to launching your business, you'll need to develop a business plan to see if the set-up costs make sense in the long run.
Sorry to say, the days of the 5 cent lemonade stand are long gone