I'm suprised people still change money before going abroad.
Surely you have a VISA account? If not, get one, and just use ATM's. When I visited Florida in 2008 I paid by card at the parks too, wich was even more convenient.
If you're with a crap bank who charges for foreign withdrawals, get a Nationwide current account with a VISA Debit card. I'm sure there are other banks out there that don't charge, but that's what I use, and it's never failed me! It may seem like an effort, but you can use it as your 'travel account' forever, and add money into it before you go away somewhere.