We let everyone we know when we plan to camp, because it inevitably rains when we go away (or is 100 degrees, or 40 degrees and gusty winds). That way they can prepare for the worst. I think we've only had a handful of trips with really nice weather over the last 5 years. We got lucky this past weekend, because it didn't start raining until we were almost packed up this afternoon. Now it is downpouring with lightning and thunder, so I'm glad everything is put away at home.
So we're used to the rain. Sometimes we go shop or out to eat. If we stay around the CG we'll watch the rain under the awning (assuming the winds are not real bad). If it's night time we'll usually hang out inside, plays cards, read a book, do crossword puzzles, or sometimes watch a movie or a TV show, but that's usually a last resort.