travelling I think the only thing you can do is be sensible and enjoy it 
Don't go for anything creamy and don't go for the stodgy pud. Don't let your eyes be bigger than your stomach. Fill up on veg etc. There is nothing worse than eating something that actually wasn't that great just cos you liked the look of it beforehand etc.
I sometimes have a pot of tea for pud, so when everyone dessert turns up I'm given something as well and they usually give you a choccy mint or something as well.
But it is only one meal out of the whole week. If you jump straight back on the healthy plan tomorrow you will do minimal damage.
This is life - there are meals and do's all the time, we just need to learn not to undo all the good so far.