Special needs diets aren't even easy when you are at home with all your stuff. They are significantly harder when you are traveling.
My ideal diet: Vegetarian (responsibly obtained ova lacto), wheat free, light on the tofu, sucrose-free, chocolate-free.
While I was in PA, I ate a lot of pizza (so lots of wheat). Why? Because there was literally no other vegetarian source. Actually, that's not true. Taco Bell has that great veggie Cantina burrito. So, I ordered one for dinner and one for lunch the next day because I knew I'd have no time to go find food because I would be prepping for the next session I was teaching. They got my order wrong (my fault for not checking, but hey, I had ordered two of the same exact thing so I thought they would get that right), and I ended up at lunch with no time to get food and no food I could eat. They had me teaching straight through the entire day (8am - 12:30pm a 45 minute break for lunch where instead of eating, I had to set up all the equipment for the next session and then 1:15-4:15). It basically sucked (the teaching was great; the no time to eat good-for-me-food is what sucked).
Luckily, they had a vending machine and I was able to get food. My lunch? A bag of potato chips and a Diet Pepsi. It was enough to get me through the day, barely, but it was pretty bad.
So, my heavens, I sympathize with people who have food allergies that are potentially fatal.
None of mine are fatal. If I chose to, I could eat meat, sugar, wheat, etc. I am better, much better, when I don't. But when I travel, I often end up with a diet that is a far cry from what I am supposed to eat.