If you're hosts won't be offended, take some wholemeal bread so you can have it as HEXB choice. Stay away from cheese on burgers. You could even take your own burgers and sausages?
If you can, have lots of salads, be careful of dressings and mayonnaise.
I find most people, when you tell them you are on SW, are pretty understanding, so if you take your own bread and stuff I'm sure they won't mind
Try not to drink alchohol, save syns for food
well, I do, I find I'd rather stick to diet coke and eat lots than drink!
Hope this helps
And have fun! Ultimately, it's only one meal, and you can always flexi-syn!