Money on hand

You really should get a debit card if you do not already have one. Make sure you have a 4-digit numeric PIN number, and inform your bank of the days you will be in Europe --what countries, and what cards you will be using.

Withdraw the money you need from ATMs. Use credit card sparingly. When balancing your ATM account, be sure to convert the Pounds to Dollars to keep it accurate. bookmark this site: www.onanda.com
go there for currency conversion, and a pounds to dollars cheat sheet that you can print and take with you.
You can wait until you arrive at the airport to find an ATM and get cash, or purchase some Euros in USA to have money when you get off the plane, and be ready to go. (which is what I do). Your choice on what you think it more convenient.

Good luck.

I'll add that many supermarkets/pubs will give you cash if you do a £10 purchase from them "cash-back" ,with debit or credit They do it for no fee as it saves them bank charges.

Also be aware, due to counterfeiting of one hundred dollar bills, some banks will not take them to change for Euros, we had to visit a couple of banks to make an exchange, so plan ahead. This was Oct. of 2008.

Some suggestions:

Open an account at an online US bank (USAA FSB is an excellent one) that reimburses any ATM fees and has no fees of their own. Fund that account with some cash. Use your regular bank ATM card and the ATM/Debit card from the online bank so that you always have a second card in case of problems and a way to get extra cash if you need a lot in one day.

A good credit card (no fees, no ripoff charges) is also good and my experience is that the charges are the same.

I agree with BG. We usually "buy" a small amount of Euro or Pounds from a bank here for when we first arrive over there so we don't have to find an ATM, and then we withdraw from ATM's the rest of the trip. We have USAA, and they are great (because of the deal with ATMs), but not just anyone can open an account with them:
Who is Eligible?
Children of USAA members.
Active-duty officers and enlisted personnel.
National Guard and Selected Reserve officers and enlisted personnel.
Officer candidates in commissioning programs (Academy, ROTC, OCS/OTS).
Former military personnel:
Retired officers and enlisted personnel.
Former officers and enlisted personnel who separated on or after 01/01/1996.

I agree with all those travelers who do not buy foreign currency before going. There are too many ATM machines and so easy to find.

I have always found one in the air terminal when I arrive in Europe; so I can buy what I need immediately.

I obtain currency every few days so I don't have to carry much with me. If you notify your bank that you will be using your ATM card in a foreign country you should have no problems.

Richard, thanks for posting about the cash back option in the UK at grocery stores with no fee. I'm sure the bank will charge a conversion fee but it is nice to know this is another option other than ATMS.