I have this issue a lot, with work travel. I meet with a few different groups but none of them mind (and why should they???) if I do go out with them and just have a glass of water. Depending on where I am, if I'm in one of our offices somewhere then I'll just go to the kitchen and make my own soup or shake and if not I'll wait til I'm in the hotel. The only place I have never asked to make my own stuff is on a plane!!! If I'm travelling longhaul I try to take a bar and have something before I leave and then when I get to the hotel the other end. I've got a whole week coming up when I'm away, there will be about 40 of us doing a huge trade show in Barcelona and I'm sure that every night there will be groups of us going out for dinner, but again it'll be something back in my room when I'm changing and water while we're out...
Boring but not forever!! And so worth it.........