Braking coefficients. I believe a number of people failed the IFR exam some time ago because these came out of the blue.
I would not say there are very few plotting question in Gen Nav. I seem to remeber about 5 or 6. I do remeber that collectively they were worth >10 marks!! Although the plotting was simple, the questions were hard to interpret and the tolerances were rather tight on a couple of them.
For Met, I believe that questions relating to castellaneous, mamatus (?? is that right) and other freaky cloud formations are rare but do pop-up occasionally.