My husband and I went on a long-weekend vacation up to Kentucy three years ago when I was in the middle of some really bad diarrhea and pain problems. I was afraid of being a downer too, so I was popping Immodiums heavier than I did when I was home all day (I was unemployed at the time). There's nothing like going on a hour and a half tour of Mammoth cave while you have this problem! Thankfully a last-minute stop at the bathroom before the tour and about three Immodiums (took the last one right before the tour) got me through it. I tended to skip breakfast and only eat a sandwich for lunch and by later in the day, I could tolerate a meal out so long as I didn't eat much fat and nothing fried or greasy. (We were vactioning on the cheap, so the sandwich thing was okay--my husband ate them for lunch too.) Because restaurant food tends to be much heavier on the grease, bad fats and butter than anything you eat at home, when you go on vacation, try to do as I did and either skip breakfast (I don't know about you, but my guts are always worse in the mornings) or eat something light, like a granola bar, yogurt or some dried fruit and nuts, then eat a sandwich and maybe some chips for lunch, then you can eat something out for supper that's not too heavy (greasy).
Avoid milk and red meat, nothing fried, no fresh fruits, no tomato or cream sauces, no caffeine or alcohol. It took me six weeks after my gall bladder was out to be able to tolerate milk and red meat and pork again. So, basically, stick with baked or grilled chicken or fish/crustaceans, no butter sauces on them, rice, bread or non-fried vegetables on the side. You can have a bit of butter on your bread; it's just in sauces that there's too much. You can have a bit of cheese. Personally I can eat salads, but some people on here have a real hard time with them, so you might try a side salad, but don't make it your entire meal.