http://www.boe.ca.gov/pdf/reg1603.pdf
Assume attendes of the reunion will be paying to attend.
"(d) PLACES WHERE ADMISSION IS CHARGED.
(1) GENERAL. Tax applies to sales of food products when sold within, and for consumption within, a place the entrance to which is subject to an admission charge, during the period when the sales are made, except for national and state parks and monuments, and marinas, campgrounds, and recreational vehicle parks.
Regulation 1603. (Contd.) (2) DEFINITIONS.
(A) “Place” means an area the exterior boundaries of which are defined by walls, fences or otherwise in such a manner that the area readily can be recognized and distinguished from adjoining or surrounding property. Examples include buildings, fenced enclosures and areas delimited by posted signs.
(B) “Within a place” means inside the door, gate, turnstile, or other point at which the customer must pay an admission charge or present evidence, such as a ticket, that an admission charge has been paid. Adjacent to, or in close proximity to, a place is not within a place."
(g) TIPS, GRATUITIES, AND SERVICE CHARGES.
This subdivision applies to restaurants, hotels,
caterers, boarding houses, soda fountains, drive-ins and similar establishments.
An optional payment designated as a tip, gratuity, or service charge is not subject to tax. A mandatory payment designated as a tip, gratuity, or service charge is included in taxable gross receipts, even if the amount is subsequently paid by the retailer to employees.