I'm pretty lax on this one. Other than the top allergenic foods (wheat, egg whites, soy, dairy, peanut, tree nut, fish and shellfish - account for 90% of food allergies) I'll do more than one at once. I try not to bombard him just so that if he did have a rxn at least I would know if it were one of 2 or 3 foods since at least that keeps it narrowed down. The point isn't that you're going to keep them from having a rxn, just that you'll know what to avoid in the future.