Bring food items that are allowed on your child's diet. It's always nice to bring a side dish or something to a party, so why not make sure it's something your child can eat.

Have a favorite "treat" food handy to "swap" for something that is offered that may be restricted. Try to use something that you know is your child's favorite treat and not given very often. Something that is reserved for special occasions. Make a deal with him/her that you will trade the offending treat for their favorite allowable treat.

Bring a new game or favorite game that can occupy and entertain. We can all relate to wanting to eat sweets and treats when we are bored and many family gatherings are based around eating and drinking, so if we can provide something other than food to offer as fun, that will help.

Attempt to inform family and friends of the issue. Obviously, we must be prepared for the fact that not everyone will understand/support and we can't expect them to change their menu or plans to accommodate, but we can let them know ahead of time so they don't fuss or push things on your child that may not be allowable.

Ask ahead of time what will be served or put out, so you can take proactive steps to either discuss with your child before they are exposed, or simply for your own knowledge so you know what to expect.

Avoid problematic foods when possible, but be prepared for the reality that something might sneak in. Be patient and understanding. Some kids have more severe reactions than others, but sometimes we just have to roll with it. Do your best, but acknowledge that you are human and can't control everything, all the time. 

I like to have activated charcoal on hand, just in case, as it can help absorb some toxins and allergens and decrease symptoms from minor slip ups.

Remember that this is a celebration and try to enjoy and have fun. I know this might sound glib to say, but I have been there. Looking back at those holiday events and parties, I was so stressed. I knew if my son had some of his problematic foods, we were all going to suffer. I was so worried and such a stress case that I didn't even enjoy any of it really. I look back at pictures and see the smiles and laughter, but didn't really take the time to grab a hold of those moments.