It varies. I don't like Burger King fries, so I will sometimes get the Hershey Sunday pie instead. LOL. Not a very healthy substitution. But I almost always skip the drink and get ice water. If I get a regular size Whopper, I don't have room for anything else. Usually I get a junior.
At McDonald's I love the fries. But I try to just sneak some off of someone else and not buy a whole order.
Same with Wendy's. I like their fries too. But that darn place has a new yummy shake.