Number 1 event of the year is Independence Day, July 4th, which is celebrated with parades and fireworks. The Declaration of Independence itself was ratified by Congress on July 4th, 1776, but not signed until much later and there could have been quite a number of other dates that could have qualified as The Day. (It is safe to assume, however, that nothing else of this magnitude has since been drafted by a commission in less than a month.)
Many Americans celebrate this holiday with a picnic. Parks have designated picnic areas with benches and BBQ iron contraptions where it is safe to burn your charcoal. Huge amounts of hot dogs and hamburgers are prepared this way every year.
You can get a variety of cooling devices, from foam boxes to mini fridges running on 12V so they can use the car outlet. Some boxes have wheels and indentations for you cans or bottles and all are taken to a park or the beach - or rather the beach parking lot. Who wants to carry a monstrosity this size very far?
You can also get all kinds of food storage bags/bins/tubs; Tubberware was started in USA for a reason. And many varieties of finished salad mixes are available at the supermarket.
It is hard to imagine this event without the fireworks. But in California you are not allowed to burn fireworks in your backyard; the risk of wild fires makes fireworks a serious hazard. Hence, firework displays are left to communal events.
Naturally, living next to a very big bay gives opportunities for watching the rockets over the water. We have often enjoyed the spectacular show put on by Port of Redwood City but from there it is obvious that many other locations along the Bay have the same - in this case literally - brilliant idea.