Yep, diet drinks and spirits are fine. As are dry whites and reds, but not rose. Beer is, very unfortunately, a big no-no. I avoid cocktails as they put syrups in and I find it difficult to judge the sugar content of all the ingredients.
I always make a point of telling the bar staff that I'm diabetic and they must use diet coke because I've lost count of the number of times they don't listen or don't care and just put full fat coke in. If you make a point of saying that you're diabetic, they're more likely to pay attention.
Make sure you take your meter out with you and test often, maybe every hour or so and take a form of glucose out with you. If you're completely smashed by the time you go to bed and you're in single figures, have some carby food. I decrease my morning Novorapid by 2 units if I had a session the night before. Oh and don't forget to take your long acting on time, so take it out with you if necessary.