It really depends on where I am and the length of my trip. If I'm in a country known for food--France, Italy, Greece as an example--and only for two weeks, I'm going to stick to local cuisine.
But if I'm traveling for a few months, and in places where food is not the main factor, I will venture into a chain for a quick meal. And sometimes that chain is non-American.
In the UK, I admit I like Nando's (I had it last night here in Belfast.) I have no problem stopping at a Paul or Pret a Manger. I prefer Caffe Nero's coffee to Starbucks and Costa.
In Chur, Switzerand, I took a nap before dinner. It lasted five hours. I woke up after 10 PM. The only open restaurant I could find was McDonalds. It was tasty.
In Kyoto, I had had my fill of green tea and mediocre coffee so a flat white from Starbucks hit the spot. (I was the only non-Japanese person in there as well as the only one over 30.)
If I'm in a very hot city, and I want a very cold drink, I'll pop in to a U.S. fast food chain for that mountain of ice in every cup. (And to use the facilities afterwards.)
After two months of a multi-month trip, I tend to get a hankering for a burger.