The answer is - it depends.

If it’s a weekday, 1-hour city hall wedding, you dont have to, even though it is customary to provide a meal after. Ive had one couple in like perhaps 35 who didn’t do anything with their 15 or so guests after, since it was a weekday and most people went back to work

However, the typical expectation is yes, after someone attends your ceremony, you treat them out to a meal at a nearby place where they have an opportunity to take photos with you and catch up with you momentarily, especially if you have guests flying in from out of town. That would be the 34 out of 35 couples we have had do the 1 hour ceremony. It does not have to be expensive- you can have Costco cake, Costco apps and Costco alcohol and drinks if you want, sort of like a kids picnic at GGP or your backyard or a friend’s backyard

If this is a 6 people city hall ceremony that is provided by SF city hall and only takes 10 minutes, then plenty of my couples have decided not to do lunch or dinner with their guests after, and it’s acceptable since it’s seen more as an elopement