I had a scan through the Food Directory, but under Smirnoff for example, there was only Smirnoff Ice. There isn't a place where all drinks are listed together is there?
Clear spirits like gin, rum, whisky, vodka etc. are all 2.5 syns per 25ml measure, and sugar-free mixers like diet coke/coke zero, slimline tonic, and soda are free.
Depends if you are aiming to relax a little or get drunk a lot, I have switched to 50ml of Martini Extra dry at 2.5 syns a shot with either diet lemonade or slimline tonic this is fine for me as I like to just have a drink to relax rather than get really drunk.x
Good luck.