I've been known to cancel getting my hair cut because I'm afraid I won't be able to sit in the chair for any length of time. I make dental appts only after 1pm for the same reason (and cancel half of them!)
Immodium and I are best of friends. I buy in bulk and usually end up taking it at least 4 out of 7 days. If I have plans I will not eat the day of, and also watch what I'm eating the day before (nothing greasy or spicy or known to give me problems).
I flew to Florida, did not eat til we arrived, made sure my seat was close to the bathroom....and wore Depends.

Plus a sanitary pad. If I could have found rubber pants, I probably would have worn those too! Figured the more absorbant material between my *ahem* butt and my pants, the better.
I also carry another pair of underwear and toilet paper in my pocketbook... just in case.
Good Luck...and try not to dwell on "what if".... chances are nothing will happen and you'll have a great time! Keeping fingers crossed for you.