I also tip an extra dollar (or $2) per drink. I take enough one's to count out 15 each morning and put them with my Sail & Sign card. Then I always know how many drinks I've had and when I'm getting closer to the 15 drink max (no judgement please). If I have special bartenders and servers, I usually tip them extra during or after the cruise. For exceptional service, I write a thank you note (pack of 8 from Dollar Tree/$1.25) and include $5's, $10's or sometimes a $20, along with a handwritten note of appreciation. This is not to pressure anyone. This is what I do and feel it's well worth it for the amazing service!