Take new $100 bills. Wallet folds can cause the bill to be refused, however, no such problems on $20 bills.

Also note that money establishments or banks will not accept torn notes £ UK Pounds or $ Dollars and you're only allowed to take in a limited amount of cash in dollars, etc. Check before you travel and don't try to be smart because as the laws state you can have everything taken from you if you do not declare what you have.

The rate is around 20 hryvnia to the dollar and the uk pound £ is 34. The value of the currency fell in February 2015 when the central bank moved to a floating exchange rate. 

Banks and cash points are widely available. Some will only allow small amounts, others will allow bigger ones. Prepaid visa cards are also good use as a safeguard back up.