Dana didn't mention a slush fund. He does tell about the captain having coffee, but being unwilling to provide the crew with any. I can imagine other ships having crews buy coffee and other small luxuries in some of the ports they visited. Of course California ports had only hides to sell.
The captain would not have allowed liquor broght on board.
Dana's vessel was bound by a Temperance regulation. The more I read of the horrible conditions he had to work under, I marvel that he ever went to sea. Imagine having to go aloft in total darkness, bare handed in freezing weather, with a toothache so bad he couldn't open his mouth far enough to eat anything but rice, which the mate stole for him from the captain's mess.