I don't know if they still do, but Fred.Olsen used to charge for Hot Drinking Chocolate in the evening, even though it was simply poured from a flask in the same way that tea & coffee was.
They were also the first line we found charging for shuttle buses, even when provided by the port authority
Most people fall for the champagne sailaway drink once, and once only. I have noticed that many lines now display the price on the serving trays and can only presume that is becasue of all the bad feeling it caused - "welcome on board, hey we've ripped you off already".
Finally for us Brits in particular, USD based ships charge around 3% fee to convert your on board spend into GBP. So we always make certain that we find a box on the form to say "keep in ship currency".
Last: Cunard Queen Victoria January 2016
Next: Oceania Nautica Aug 2016
Then: P&O Oceana December 2016
Golden, Grand(2), Caribbean, Royal, Sea(4+1 aborted)
Adonia(4+2), Arcadia, Artemis(2), Aurora(5), Azura(2), Britannia, Oceana(3), Oriana(12), Ventura(2), Victoria(5)
QM2(2), QE2(9), QV(7), QE, Caronia(2), Minerva, Minerva II, Fred.Olsen(8), NCL Jade, =X= Eclipse, HAL Ryndam, Aza.Journey