In three different companies, I had to submit reports to the board on a monthly basis. I started putting in a line that said "if you read this, call me and I'll give you £XX". I started at £10, and went up by £10 per month. Nobody ever called, nobody ever mentioned it.
A friend did something similar, except it was a bottle of whisky mentioned in the middle of his master's thesis. Just before starting his defense, he put a bottle of whisky on the table and nobody claimed it.
@michael @fesshole I probably would not take alcohol from a student whose work I was hired to evaluate, for several reasons
That's a fair point. Though many Danish master's student/supervisor relationships are closer to friendships. I would definitely have claimed and then refused the bottle.