The last time I was in England was 2004, and I got along pretty well with my Visa credit card and AT&T Pre-Paid phone card. In fact, the latter worked quite well. I might have been paying 20 cents a minute to call home (Calif.).
How about Ireland on these matters? I will be traveling only between Dublin and the Dingle Peninsula.
I presume the internet is pretty available at most lodging, and places. I recall when I was in Conway Wales that I stayed in two RS recommended places, and had internet.
I don't think I need Traveler's Checks. Just convert to the country I'm in at exchanges, then back to US $. My itinerary is simply: London for a few days, Ireland for a week, then back to London for 4-5 days.