If you are going to be with a group of people with various allergies I'd only bring an assortment of "fresh" products (all in separate containers - nothing mixed). You can buy small containers in Dollar Bill Stores. Make up different cut up fruits or veggies, each in individual containers. I'd also take things that I know that I can safely eat - for myself and/or family. Or check ahead with all going to picnic and plan accordingly.

Like the others have said; the less processed, the better. Try to stay away from the most common allergens if you don't have specific allergy information. I would bring a variety of fresh fruits and veggies, separated if possible to avoid cross contamination.

Veggies and fruit trays also when you make a covered dish make a list of all the ingredients.

I always brought safe foods with us. It really depends on the allergy. Corn allergies are the most difficult because it is in so many foods. Then fresher and plainer the foods, the easier it may be. Don't mix foods up, keep them in separate containers, if you bring prepackaged foods make sure the ingredients and allergy information is available for others to look at.

As a side note: Baby Carrots have a lot of Corn contamination and the pre-made vegetable platters have some Corn contamination.