Couple of ideas from my own similar experience:
1) Allergy testing does help. Even if you have to wait a year, get that scheduled asap.
2) My allergist put me on a restricted diet for 2 weeks & then had me introduce one new food per week for each week after that. Takes a long time, but it got me good info about my allergies. The 4 foods he always starts people on spell out B-R-A-T:
Rice (white is best, but can be anything as long as it's unseasoned)
Applesauce (100% Natural, or make it yourself -- No Corn Syrup, sugar, cinnamon, flavorings...)
Tea (must be herbal since caffeine is a major allergen) -- no sugar, creamer, honey, etc.
Also, make sure you are not drinking your allergen. Besides tea & water, my doctor let me do 100% Apple Juice, not from concentrate. I don't like apple juice, so I would cut it with 1/2 water.
For the Tea, I recommend Hibiscus Tea (Panera makes a yummy Hibiscus Tea). It's naturally a little sweet so you don't need sweetener. Also, probably not good to pick Licorice Tea for first 2 weeks since people are often allergic to licorice. It is good, though & doesn't need sweetener either.
The best way to prevent allergic reactions is to cook for yourself. As much as I love Chicken McNuggets, too, there are just way too many potential allergens in there: batter, preservatives, natural/artificial colors or flavors, oil(s) in which they're fried, whatever's in the sauce, not to mention the potential for cross-contamination at any point in manufacturing, transportation, storage or cooking process, plus the fact that Purdue admittedly uses antibiotics and steroids on their live chickens (Purdue supplies the meat for the McNuggets), so there are just a whole lot of possible causes of your allergic reaction.
In order to best rule out allergens, you want to limit ingredients as much as possible. Choose whole, organically-grown fruits and vegetables, and fresh, organic beef/chicken/pork/fish (and if you can tolerate it down the road, seafood). Wait 1 month before introducing anything with wheat since besides the fact that wheat can be an allergen, gluten intolerance can make you more prone to react when you come into contact with other foods to which you are allergic.
Once you've been at it for a good 4-6 weeks, you can try some kind of simple bread with limited ingredients. Because preservatives are difficult to control for, fresh bread from the bakery is your best bet. You can always freeze half of it so it doesn't go bad. You can look up "Allergy Elimination Diet" for better lists of what to include or avoid in those initial weeks, but basically, just stay out of the middle of the grocery store and don't eat at restaurants. Also, you probably want to try avoiding iodized salt (regular table salt) for a bit. There's plenty of it in Chicken McNuggets, incidentally, and it can sometimes cause allergic reactions up to & including anaphylactic shock. My brother has that problem. Instead, we use Sea Salt or, sometimes, Kosher Salt. Be careful because the last time I was at the grocer, I saw there was one type of Sea Salt where they actually added iodine.
Hope that helps. I feel for you. It's not fun to go through the Elimination Diet, but at least you usually just have to do it once like every 20 years or so. :) And it's worth it not to keep landing in the ER.