Good advice Thomas!
One other thing that I have done in the last few years is to open a separate checking account that is only used for travel. My banker suggested this. You will receive a separate ATM/Debit card for that account. I have never bothered to even order checks for that account.
Make sure that checking account cannot access any of your other accounts. That way only the amount in that account can be touched. You can move money into and out of that account as you need it. I will put one or two thousand into it for travel and if I need more I just get online and transfer more or if there is money left at the end of the holiday, I just transfer it back to checking, savings, or whatever account I want.
Once again, I echo what most folks have said. Don't bother going to the bank or foreign exchange booth. Just take out money at the airport, from a bank ATM. Depending on your bank and type of account you have you will probably save money.
On my Wells Fargo account I get the current "actual" exchange rate and the non Wells Fargo ATM fee is waived. Otherwise it would be $5/transaction. Most accounts will charge a non-bank ATM fee so take out enough to get you by so you aren't paying the ATM fee over and over. I.E. Don't just take out 20 Euros.