Try wine! Fewer carbs. Or a whisky neat or on the rocks. Tonic is full of sugar, so I'd stay away from that (or at least in Canada, tonic is full of sugar). Or if you want bubbles, alternate sipping alcohol with a glass of "soda bitters" - just unsweetened bubbly water with your choice of bitters. low carb, tasty, and keeps you hydrated!
edit to add: also, eat a good dinner before you go out, have better-for-you snacks available, and don't overdo the booze! i end up eating unhealthy snacks if I have too much to drink, cuz i make worse choices, and am hungry due to lower blood sugars from the booze.