Don't wear white or wildly-colored athletic shoes. Obviously you're probably going to have some kind of Nikes, Reeboks, whatever...but try to get them in a quieter, neutral color...you won't be screaming "American tourist", and they'll go with more of your outfits. I'm a girl, so I don't know exactly how to tell a guy to dress in a pub...others will probably be along with good ideas. In the U.K. and Ireland, first with my dad and in later years with my husband: They just wore the same things they wore in the States. They looked like everybody else. Let's see....collared shirts tucked into belted, casual slacks. Comfortable, leather walking shoes. Hip-length casual jacket, water-resistant, in a conservative color. They had a sports coat to put on in the evenings, which didn't get a lot of use. A tie...ditto. Make sure you have rain gear...but you know that.