I've always had to deal with some allergies/sensitivities. Since I've been an adult, I've been unable to eat oats, and currently I carry an epi-pen just in case I get accidentally exposed to them. No big deal with that - my main problem is remembering that the epi-pen can't be frozen, and I therefore can't leave my purse in the car. Both of my kids seem to have inherited this sensitivity (I feel like I should apologize to them).
I'm also unable to eat potatoes. This is a bit more of a pain; they taste really good and they're in lots of things. I do eat them occasionally (mooching the odd french fry, eating perogies, etc.) I'm usually sorry later, but I can deal with that. I know it's my own fault, and I remind myself not to do it again.
I'm lactose intolerant as well. I can eat one small yogurt a day, two is too many. In the same way, I can eat a little bit of cheese, but need to take a lactose tablet if I eat something like lasagna, which has lots of cheese. I use rice dream instead of milk on my cereal in the morning (soy milk may be cheaper but it has the same effect on me as milk, not fun).
All of these allergies or sensitivities are almost second nature to me; I've lived with them so long that I don't really think about them at all. When I cook at home, I don't think of them at all - when I am eating at other locations, I read labels, ask questions, and am a little bit more careful.
However allergies and sensitivities are becoming more and more common. When I have the family over for our regular meal together, I'm now doing as many as three different variations on the same meal. Ruth is trying out wheat free (or maybe it's gluten-free, I need to check) at the recommendation of her naturopath for the next while. My dad has also gone wheat-free and has found it has really helped his health. Rachel and Joe are milk product free (I use soy cheese for them). Nicole (my boarder) doesn't eat beef at all. In addition, Ruth is diabetic and has high blood pressure (low or no sugar added whenever possible, low sodium whenever possible).
So, if I'm making something like lasagna I will make the main casserole for "everyone else" - layers of meat sauce, cottage cheese and spinach, topped with grated cheese. For Nicole, I'll make a small individual lasagna with soy meat instead of hamburger, but everything else the same. For Rachel and Joe, I'll make a loaf pan sized lasagna for them to share, with only meat sauce and soy cheese on top. For Ruth (and Dad if he's visiting), I'll make individual lasagnas with rice noodles instead of whole wheat noodles. I now make my lasagna with low sodium canned tomatoes or tomato sauce (the regular stuff can have as much as 540 mg per half cup!). That's four different types to keep straight!
It is easier to do all of this because I do cook most things from scratch. However, cooking from scratch generally means that I do open cans; cans of tomatoes, tomato sauce or whatever, occasionally canned soups (cream of mushroom or tomato), bouillon, etc. I'm finding it more challenging all the time though.
Today for supper I'm making homemade chicken soup. Right now I've got the chicken on in the slow cooker. When it's cooked, I'll remove the meat from the bones and add them back. Then I'll add in vegetables (carrots, celery, onion, etc.) Before all these food restrictions, I would have likely made homemade dumplings or noodles to go in the soup. However I think I'll add lentils instead. They'll still add the body to the soup, making it more filling, but no one I know of is allergic to it.