Everyone handles these situations very differently. Here is my experience and what has and continues to work for me. My career (sales/financial services) is all about wining & dining - alcohol is everywhere. I found that being able to mentally prep myself prior to dinners, functions, etc where alcohol is prevelant helps tremendously. I know what the situation will be like and have a plan in place in case things become 'difficult' for me. Many people have asked me "oh, you dont drink - how come?" I love to respond with humor - "Actually, I am a professional drinker" is my favorite.
You know what the scene will be like and can prep for it ahead of time. Show up with a 6-pack of perrier or soda maybe? Have a plan B if things become hard for you.
Best of luck.
G