I agree with Shawn - those items sound the safest. And with checking if they make special meals. Doesn't hurt to ask!
Also, take with you your soluble fiber & some tea (peppermint, chamo, etc. - your fav). Maybe have a small, safe snack before you go to dinner to buffer your tummy also.
And, try not to get stressed - I know, easier said than done. Try to focus on how much fun the concert will be!
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Re: Going on a trip
Try to focus on how much fun the concert will be! 
