I eat at McDonald's and Wendy's. I order Double Cheese burger with no bun and french fries. Wendy's actually has a gluten free menu as well.
I'm not sure if you're American or Canadian but we're personally in Canada and I know the U.S. fries are not safe at McDonald's.
I was diagnosed at 27 years old, shortly after my wedding. I'm not saying it's easy but it's something that is in my opinion very manageable.
If you and your son happen to live in the states you should know that Burger King USA offers a Gluten Free Menu: http://www.bk.com/cm.../GlutenFree.pdf
Otherwise you could take a read of the Canadian ingredients and see if you can order a burger there: http://en.burgerking...ndAllergens.pdf
From a quick glance it looks like they may have some options!