Even the simple French fry can be fraught with gluten dangers.
However, some fast food restaurants are better than others.
McDonald's French Fries are not only fried in contaminated oil, they sprinkle gluten-laden stuff on them made out of wheat. McCeliac McDeath. AVOID.
Wendy's French Fries are fried in oil with other glutenful items, but at least they don't sprinkle wheat on them. AVOID. (However, the baked potatoes are a good choice.)
Burger King French Fries really are GF! They're sprinkled with salt, not weird concoctions, and fried in a seperate fryer dedicated to french fries. GF King of the Celiacs. Let the rejoicing commence!