Exchange rate

I have Not seen a major difference in exchange rate with Italy over the past 8 months. I always buy Euro here in the US at my bank before I fly out to Italy, enough for food and drinks, taxis, and a few days time for me to locate a bank's ATM in Italy.
Talk to your bank about buying Euro and the Pound. Ask your bank for advisement now. Buying International money should Not be done at the last minute. Get familiar with different money as soon as possible and you will feel like a pro before you leave, more in control.
You will want to use your Debit Card to obtain Euro from bank ATMs in Italy, Not your Credit Card. Talk to your bank now about any transaction fees that may apply. Withdrawing large amounts of Euro at a time helps keep fees down. Only when I was on the West coast of Italy, I could withdraw 500 Euro, but on the East coast, only 250 Euro within 24 hours.
I used 2 Debit Cards from 2 different accounts (at the same bank in my case) to help get the Euro I needed. One card had a transaction fee, the other had None.
I buy Internationally from Italy even now that I am back here in the US. When i use a Debit Card, i pay No transaction fee, but when I use my Credit Card, I pay a high transaction fee. Again, take advisement from your bank.
I used my Credit Card in Italy when websites or Individual B and Bs asked for my Credit Card to reserve a room. But then I would pay the bill in Euro cash and my Credit Card never got charged.

Noah, It's a crapshoot. Get 100 British Pounds before you leave and use your ATM/debit card in Italy and England for your further cash needs. DO NOT use a credit card for cash. That will cost you much more.

You have time, so think about getting a Charles Schwab account for the trip. Easy to open, and there are no fees for any withdrawals, ever. Also, the Capital One CC has no international transaction fees so an excellent choice for things you have to charge.

The cheapest and most convenient way to obtain local currency is via a debit card at a bank owned ATM in Europe. Take a hundred pounds with you to get started. Any bank, Am Ex office, or even a currency exchange bureau at an airport will get you the pounds but you will pay in the range of 10% for exchange in the US but it is worth it for the convenience when you hit the ground.

Oh, I see you want to be a currency speculator. If you get it right, you could make millions on Wall Street. But there are innumerable factors effecting the rate. Besides, talking about a hundred pounds, the variation is liable to come to a whole Starbucks Mocha Grande. If your bank and credit card charges the "usual and customary" 3%, that is liable to be a bigger factor and it is one you can control, as the other posters have pointed out. The "usual and customary" only happened about 10 years ago when the banks discovered it as a way to squeeze more money out of their clueless retail customers. It is starting to change now as the customers are no longer so clueless.
Any foreign trip involves speculating on the future value of a commodity (your $) that may be beneficial or detrimental to the original cost estimate you made up. So once you have made up your mind to take a trip, and you can afford it, start planning and dreaming about how much fun you're going to have.

George Soros would probably say it's crap shoot.
Just get enough money for your first day, just in case you can't see an ATM immediately, then use your ATM card. Just call your bank and notify them of your travels or they mightblock your card when they see international usage for fear of fraud.

First, notify your bank and credit card companies that you will be traveling and using your cards so that they don't block your transactions in Europe for suspicious activity. Call again a few days before you leave to make sure this was done.

Then, if you want to have cash on hand when you arrive, order some Euro and some pounds from your bank - enough for your first day. It may take a few days if your bank doesn't stock foreign currency. I would not order just pounds and then convert the remaining ones to euro (these types of exchanges tend to cost a little more on the conversion rate). On the other hand, you are not talking about a lot of money, so do what's most convenient for you.

Thx everyone. Im gonna get between 50 and 100 euro before i leave just so im not SOL when i get there. Thanks for the tips on the cards, i will check on those.