One of the problems for allergy sufferers is that there are a lot of common (and some less common) allergens that are hidden in prepared foods like seasoning mixes, canned soups, ketchup, salad dressing, and things like that. So using prepared foods as ingredients pretty much guarantees that people with allergies won't be able to eat what you brought. If everyone is including those kinds of ingredients (and most people do, because it's easy and convenient), that means that allergy sufferers won't be able to eat anything there, except for what they bring themselves. If you want to try to avoid triggering allergies, it's best to not use prepared foods in your recipe.

Peace, I don't know yet what to make of that site you linked to, but this part concerns me...

The following daily menu is representative of the types of foods that would be included in a strict Allergy Avoidance Diet:

Breakfast:

    * Hot rice cereal with maple syrup, sliced pears, and chopped cashews

I don't think cashews can really be considered a good "strict allergy avoidance" food. For one thing, it's not uncommon for them to have some peanut oil on them, and also because cashews themselves can trigger some people's allergies.