You've got your people who are lactose intolerant (at least 3 of the 12 members of the group* on saturday!), which is apparently a huge chunk of the population. A lot of people are allergic to nuts (my brother, for one, and my cousin, for another), or shellfish, or this, or that. My wife had a friend who was allergic to garlic (apparently he was actually descended from the same bloodline as vlad tepes or some other real-life person who was the inspiration for count dracula, and that family actually is allergic to garlic, which is part of the reason for the legend - but I'm not sure if that's actually true, or just one of her stories).
Then there are the vegetarians, who at the very least have a mental intolerance to meat, if not an actual physical intolerance to it. That whole no-meat thing never made any sense to me; humans, last I checked, were omnivorous, so what's with the avoidance bit? Can't say it's more natural, and really, it's not any more healthy. A balanced diet, properly prepared, is a lot more healthy than excluding such a huge variety of foods.
Then there are the more unusual and mysterious things out there... things like irritable bowel syndrome, or celiac disease (intolerance to gluten, i.e., basically all wheat products).
Is there anyone that can just eat stuff? I think I may be the only one left on the planet. Dear Lord.
* - It was rather amusing; during dessert, everyone on the side of the table I was sitting at (other than me) had some sort of food intolerance. 1 ibs, 3 lactose intolerants, and a vegetarian.