I was trying to decide which currencies to bring as well.
After reading some of the "boards", it seems that we will be able to use left over currency from one country to exchange for the next country's currency. Makes perfect sense!
You can easily do that. Probably have to use an exchange bureau and will pay a fee upwards to 10% so keep the amount to be changed as low as you can.
I guess to some degree it depends where in "Eastern" Europe you are going. Generally speaking every time you change money you lose money to one degree or another. It's also more comforting for me to enter a country with at least a small amount of local currency for convenience or emergency. To that end I get some cash either at my bank in the US at a miserable exchange rate or at the airport upon arrival at a somewhat less miserable, but still lousy exchange rate. But I generally keep this to under $50. Once in country I try and rely on credit cards when possible and draw cash at the ATM when I need pocket money. Then when I check out of my hotel I pay part of the bill with whatever cash I have left. Still, I hold on to some small amount for unexpected needs on the way to the border or airport or train station or ..... Again, something less than $50. Yup, I have something less than $50 in about 20 different currencies in a box in the closet. But It's surprising how often I meet someone going the same direction I just came from and I am able to sell some currency. Countries on the euro in Central and Eastern Europe are: Austria, Estonia, Kosovo, Montenegro, Slovakia and Slovenia. As printed elsewhere here you can to some degree use Euros and even US Dollars in most of Central Europe and to a somewhat lesser degree in Eastern Europe but when you do it on a case by case basis in stores and restaurants you are not going to be getting very good rates. Check with your credit card company and see what sort of rates they will give you and what charges might be involved. Here is more information that might be helpful.
http://budapestflat.shutterfly.com/ Look in the upper right hand corner for Links to Currency Decisions in Europe. One link is an article the other is a link to the Master Card exchange rate site. Bottom line: You are on vacation so do what is most comfortable for you and enjoy!