Pam, you might consider the "easy-going theme" and have a backyard picnic.
Don't know how many folks you're thinking about or the venue: will you have access to a backyard? A beach pavillion? Easier on the clothing options too. Um, that was "type of clothing" option, not "lack of clothing" option.
Or hey, that could be a whole 'nother theme.
A few years ago I planned a long-distance reunion with 10 friends by using Costco's online site. I planned the menu in Florida, flew out to California for a vacation, flew to Pittsburgh, rented a car then went shopping at Costcos for all of the picnic needs: food, desserts, salads, drinks, table covers, etc. Got everything I needed except the silverware as I only needed silverware for a dozen, not 500 people. I also stopped at a nice bakery and bought interesting rolls.
I pre-arranged with the B&B we were all staying at to use their frig and freezer. I reserved a pavillion at a state park and then we all went on a boat ride at their lake.
Costco has lots of prepared food choices reasonably priced. I avoided anything that needed to be heated: we had meat/cheese platters, fruit platter, several salads like Caesar, layer cakes, pie, cookies, bottled water, bottled Starbucks, etc. Since it was a state park, we weren't allowed wine/beer. That was later at the B&B.
Wedding cake can be preordered from an LA bakery...or maybe a happy wedding cupcake option?
By the way, congratulations Mom!
(PS: I just linked Costco's website. Geez, you can even get a casket there now. I'm somewhat speechless at the moment...)
http://www.costco.com/Common/Category.aspx?cat=3605&eCat=BC|3605&lang=en-US&whse=BC&topnav=