Ezybus, actually, no, I don't usually. Because I know that buying 3 bottles of grog is going to put me way over the carry-on weight limit so I don't buy it. If I just have a tiny handbag with me to carry on then I might buy something, but I'm not going to go over the weight limit just because I want to buy grog a bit cheaper than at home...
Is it really so hard for people to see how having 'unlimited' weights in hand luggage is a problem?!