If you have no plastic card (either a debit, or a credit one) and do not wish to be bothered with travelers cheques (where commission charges tend to be quite high) you will be better off taking with you determinate currency.
At present, these currencies are clearly Euros (#1, offering the best exchange rate) and US Dollars (as widely accepted but somewhat marked down by the Exchange Bureaus & banks due to the recent slide).
Some other currencies are accepted, but they are heavily marked down.
Favorite thing: Everybody (well, almost!) likes receiving letters - I certainly do, though there are other, more modern and efficient means of communication - e-mail, phone, and such like. However, if you simply like getting letters or if you need, say, the originals or paper copies of some documents sent to you while you are on the move, you can use the poste restante service. Your best bet is to use the American Express service, which is available for free to clients - you should hold either their card or travellers cheques. They are reliable and present in all major cities.