Hi and welcome to the forum. Hmm, that is a tough one. This is definitely one for the doctors. There HAS to be a solution, MILLIONS of people suffer from IBS, I am certain there is something that can ease your pain/symptoms while out.
now, that doesn't take care of the anxiety issue, but the good news it, there's a pill for that too! Or, if you prefer something natural, there are ways to curb your anxiety such as meditation and exercise, you can also look into hypnotism to specifically target your food and travel anxiety.
I suffered horribly with IBS when I was in my early 20's, to the point where I was visiting the ER about once a week the pain was so great. I had c-sections for the birth of my two children, but a friend who went through full labor and childbirth and also suffers from IBS said she would go through labor and childbirth again any day over the pain associated with IBS, it is truly horrible, I sympathise.
The thing is though, it is proven- both scientifically and through user experience, that your anxiety is 99% guaranteed to get better once you clear your system of alcohol. Bowel issues also get better.
IBS is something separate and different though, so again, I would suggest seeing your doctor. You deserve relief and you shouldn't have to find it by abusing alcohol.