Cliche but you really just need to be confident in your decision to not drink, and be someone who can hold their own and be interesting in conversation without alcohol. Truth is even in the upper level of the business world, a lot of people drink at events as a crutch to be more open and conversational.
It's incredible the number of corporate golf events or charity galas I've been at where executives are very reserved and almost timid in conversation at the beginning of the event, but by an hour in are as social and talkative as can be.
I think the stigma of not drinking in the business world has declined a lot over the last decade or so. Most businesspeople you'll run into really won't care, as long as you can be naturally sociable and fun to be around. I don't even recommend mocktails or "non-alcoholic beer" (honestly drinking a bottle of non-alcoholic beer might make you look more lame than just drinking water).
I was in a similar position as you, where in the past I would drink a lot at these events, but realistically beyond 4-5 drinks my ability to coherently talk about business would begin declining. I've cut back significantly, mostly for health reasons / mental ramifications, but if you're really concerned about appearance, nursing one drink isn't the worst idea. We always tend to overestimate how much other people care or think about details like this.
