I'm not sure this is very helpful, but whenever I'm in a public situation with people and I can't control the food, I try not to make a big deal out of it, and just eat small portions. (It sounds like you did this.)
I find it actually ends up being counterproductive with a lot of people if you say you're trying not to eat much, especially for 'special events' like vacation, because they'll take that as a challenge to get you to 'let loose and have a little fun'. They mean well typically. So it's almost easier to fly under the radar and just eat bits of this and that.
Only thought is maybe recommending / bringing fixings for some salads and really loading up on that to fill you up, while sampling other things so people aren't offended. If EVERYONE else hates salad this may be a little weird, but if you bring a few different kinds of dressings and then just stick to the healthy ones, surely there is someone else who would try it?
Anyway just some ideas.. it's tough I know! My family can't eat out without going to a basically southern buffet - where who knows what the calories of so many things are. Do your best and recognize that 'life happens'. Don't let it keep you from having fun.
Also if you end up with another 2lb bag of M&Ms, I'd recommend bringing them out to share with everybody. Have a few yourself, but just a handful. I could also see myself secretively dumping some in the water but that may be a little extreme. :cough: