Amen to Vrapan's comments. Milk Bar is also good.
All the chains turn out is buckets of hot milk, with at best a very weak taste, usually a very weak, bad, taste. The espresso, neat, is undrinkable. Really, really rank.
…and yes, if I'm going to somewhere I don't know, I will do a bit of research first, and find out where's good. I'd far rather not drink any coffee, than drink bad coffee. Most of the time I stick to what I make at home, which is made with fresh, non-burnt beans, and is way better than any chain, and not far off the gourmet places.
For travel, the Sainsburys coffee bags that someone else mentioned aren't too bad, or I'll take a Cafetiere and some preground stuff, although that's far from ideal as the coffee goes off after a couple of days.
For all the detractors, I'm into coffee the way some people take wine or whisky seriously. Maybe it is poncy, but that's my decision.