They were selling bottles of satsumaimo (sweet potato) flavoured happoshu (a Japanese beer-like drink) on board. Satsumaimo are a famous local product. 'Satsuma' is the traditional name for the area; this is also where the fruit of the same name comes from.
(The drink was awful, by the way...)
I apologise in advance if I'm tardy with commenting on your blogs or returning comments during the week... I will get to you though!