The names of the people who paid for the painting. "Eighteen names appear on a shield, painted circa 1715, in the center-right background, as the hired drummer was added to the painting for free." https://en.wikipedia.org/wiki/The_Night_Watch#Commission
If I was on a night out usually I wake up quite early, like around nine. Then I feel the hangover of course but I don't go to bed again, instead have my coffee and start working. That day I feel tired and less energetic but I know of course that this is from the nice night out. When I arrive home at night I'm longing for bed but don't go to bed anytime sooner or later than I'm used to go, which is around half past 11. Then I sleep in within a short amount of time after having read a few pages in a novel. That's my hangover day novelty.