Read response #15 then katafrass. Then get the right cards to use.
In general, using credit cards to pay for things and a bank/debit card to withdraw cash from ATMs will ALWAYS get you the best exhange rates. Forget carrying a lot of cash, forget travellers cheques.
Take a couple of hundred $ in 20s for emergencies. Take second cards as backups and keep them separate somewhere. Take photocopies of your cards to help report them lost or stolen. Or scan them and download them to your e-mail account so you could print them out if needed. Do the same with passport,driving license, air tickets, etc.
Depending on where you travel to, you have to use some common sense regarding getting cash along the way. If you are heading for some truly out the back of beyond place where you are not likely to find an ATM then obviously you need to get cash out before you head there.
Just know cards are the best way to access your money and some cards are better than others for exchange as shown in the link in #15.