I already received a couple of questions regarding money. Do I carry all cash with me? How do I exchange it to local currencies? How do I protect myself from being robbed?
So, of course I don't carry everyting in cash. There are more and less developed countries but everywhere you can find at least one working ATM machine. The only questions are how to find it (sometimes it takes a bit of searching) and what are provisions like? Some banks offer fixed provisions, some based on the amount you are withdrawing. For citizens of US you can find banks without provisions at all! So, just make some research, get information from all banks where you can open account and calculate which is the most convenient for you.
In general, there is a rule: more money as we withdraw in one action, less money we lose with provisions. I definitely don't recommend to withdraw amounts below 200€. Don't think much if you'll spend all this money before leaving the country or not. On every border crossing you will be stoped by local money dealers. But check currency rate in advance. You will probably find the best one by non-official dealers. I don't trust much offical exchange offices. Everytime there is some additional provision that they don't tell you before you pay. The only official place where I would exchange money is a bank!
Even though we have sometimes a different feeling, 99.9% of people in the world are honest and fair. Anyway, you still can become a target of one of those 0.1%. And you have to protect yourself from being robbed or to stay without a credit card as your only way of getting money. The solution is easy. One credit card should not be your only way :)
For longer trips I advice you to use at least 3 cards. First one you carry always with you - it can be in a wallet or even better in some more hidden place. Second one I hide in a smaller backpack, which is also always somewhere near me. But the third I keep in a bigger backpack that I leave in a hostel or at my host.
On account of any of those cards I don't have more than a couple of hundreds of euros. Majority of my savings I keep on main banking account. Card for this account I left at home. When I spend money on other cards I just transfer new amounts using online banking services.
Additionaly I recommend to have also some emergency amount of cash with you. US dollars are the best, because it's the only currency that you can be sure to be able to exchange anywhere. Including Northern Korea :) Again it's smart to spread this money to different places. For a couple of euros you can buy a trousers belt with hidden pocket on e-bay. But with some imagination you don't need to buy anything. You can put bills in a small waterproof bag and sew it under inner side of your jacket. Or in shoes. My favorite is under a patch on a backpack. The only thing you have to keep in mind is that it can happen you will throw that backpack someday away. That time you have to remember it might be more valuable as it seems :)
In my opinion, wallet is the most critical part and it will be the first target of all pick pockets. You have two options. Eighter you figure it out how to protect your wallet from being stolen. Eighter you don't carry in it anything without which you can not survive and you don't need to worry what happens if it gets stolen. I have my wallet always in my pocket. But in it I carry only about 20€ in local currency, couple of bills and two credits cards that expired last year. I can handle losing 20€, cards will be no use for anyone, and the wallet looks like my only source of money. I never had to do this, but I have an idea that if I get attacked I throw this wallet to teh robber, run away and hope he will be satisfied with contents of it. Valid cards, the rest of cash, passport... I carry in a pocket on the inner side of trousers. It looks like on the photo below right. You can buy it on e-bay or sew it by yourself. Mine was made by my mum (thank you mum :D)