Right, I always say that the secret to successfully getting through one of these 'events' is planning.
Have a plan of what, ideally you would like to do; be it sticking to the plan or using the add a meal principle...
Then you should have a back up plan if you get there and find it's mission impossible!
I tell my clients to phone the venue before the day of the event and ask what the menu is... then usually this is what's easiest.... Ask them to make up your 'special soup' for starters and serve you up a lean protein and veg main course.....Nobody will notice whether or not you eat the main course, you can if that's your back up plan! And nobody cares if you have a sweet or not!
Personally I find it easiest to let the waiter fill your wine glass and then drink water from another glass... but I understand that some would find it impossible to leave alone, so that one is up to you!
Remember Perfect Planning Prevents P!$$ poor performance!!!
Hope this helps somewhat.