The fireworks. Regarding deblipp's answer - I once went camping at Whiskey Lake in California with a co-worker and some of his friends over Independence Day weekend. We returned on the 4th, and driving along Interstate 5, we saw fireworks in one town after another on the way home. We didn't see anywhere near 27, but we saw more than the average number.
Another time, I spent Independence Day weekend at the youth hostel in Long Beach, CA. We saw a double display; one over the LA Coliseum, the other over Disneyland.
A few years ago, I took a sports photography course at High Cascade Snowboard Camp. This was in late July, so I called the camp to see if there was a way to obtain fireworks to tape to the back of the shredders' boards. The nice guy who answered the phone told me fireworks were not allowed at camp, since it is in a national forest. When I got to camp, my coach introduced me to Preston Strout, one of the owners, and he said, "Actually we already met over the phone! You're the one who was asking about fireworks!" He is a former pro shredder himself, and he sounded as if he wished he had thought of that before having to assume so much responsibility.
The following year, I attended HCSC in late June. After Session II ended, I stayed in Portland a few days, and on the 4th of July, witnessed a triple display.
These are my favorite Fourth of July memories.