I had to do my brother's 40th recently. A whole day session in the pub with family, friends, everyone drinking.
A really long meditation before hand help me a lot, and I also had a couple of self-care days leading up to it. Not letting stress creep in and doing tons of walking. I know that might be harder for you as it's your party but try and factor in some of that stuff into the run up, as it will help you manage this from a place of calm.
I also concentrated on how awful everyone looked once they's had a few drinks. They started to look distorted and we speaking utter rubbish. That helped me tap into some grateful thinking. A safety/exit strategy also sounds like a good plan. Try not to worry too much in the run up......you can do this!