Take US$ to use in Russia. You can change up amounts on board - or we just got out a small amount around £20 each day from an ATM. Estonia takes EURs as do most countries.
If the countries use something other than the Euro, in the main, they will except them although you may lose a little when they accept them and you may get change in the local currency but it is seldom a problem even when doing your own excursions. For any major purchase use a credit card and preferably a Nationwide one as it's much cheaper than the rest. Ida.